I’m in medicine; not psychology, but I do show many of these posts on here to Friendster comic relief. One happens to be a child psychologist.

She said that mental activities that make them think and choose on their own are the best ways to build critical thinking skills at a young age. Give them an end goal and let them figure out how to get to that end goal with little to no direction on exactly how to get there. Point out mistakes or better/different ways they could have done it when they’re done. Have them explain why they did it the way that they did without criticizing their logic. Also, don’t make it a job for them. Keep it fun and don’t force them to do things that they don’t find fun. When they start seeing it as a job, let them stop.

~Legos And/or erector sets with a task to build particular items that makes them figure out on their own how to do it best and make it look best. If they could do it better, point it out in a fun way so they think a little deeper each time they do it.

~Art; drawing, painting, music, etc. Give them a goal and let them go. When they fall short, show them new ways of getting there then let them do it again. Make it fun and not an assignment that they have to do, but something they want to do.

~Math projects starting at their level and building up to complex math problems with much more teaching and help up front.

Mine was art. Didn’t think of it as building critical thinking skills, but I got my bachelors on an art scholarship, so it at least did that much. My brain does start firing several steps ahead with a pencil in my hand though.

Instead of giving them the answer , step through the reasoning you use to get to the right answer .

While we want our young ones to be confident, we equally have to promote the use of the term "maybe". Kids and young people like to think they know everything. We know they don't because we know no one does. I would also promote the term "degrees of certainty".

Depends on the age of the child, skills of the parents, resources, and TIME. From my experience, both growing up, and later as an Army officer, and then as a volunteer mentor to disadvantaged young men, hands on learning supported by "book learning" is required to accomplish this very important trait/skill set. The emphasis should be focused on practical applications of "theoretical" disciplines from mathematics, physics, chemistry, logic, and communication skills. Problem solving, while a learned skill, then becomes second nature.
This set of books is only a sampling of what a parent or teacher can use to capture the imagination of even the most 'non-scholarly' child or young adult. Disregard the sexsist titles. The projects, coupled with age appropriate texts on the above mentioned diciplines have worked well for me throughout my life.

I strongly believe that logic courses should be a mandatory part of the curriculum. Depending on age, there could be a home school situation for this since you won't get it at school.

Sources, sources, sources. It is vital not to look at any single source, but to consider a variety of sources. Double, triple check information. Keep an open mind, let proof be one's guide. Interpretations, not opinions. The former are based on evidence. If you read languages, try various language information too.

My favorite method (with small children,) is to tell lies. Big, whopping, obvious lies, and encourage them to catch me at it.

"And then, I jumped up onto the roof! One jump! And there was a BEAR on the roof!"

"Huh-uh," they giggle, "you can't just jump up to the roof!"

"What? Why not?" I feign innocence. "Don't you think I'm strong enough? See my big legs? Look, I'll jump right now!" And I jump, maybe two feet off the ground.

"That's not high enough!" they shriek.

"Hmph. Well, okay, maybe I used a ladder. But there was definitely a bear on the roof!"

And so on. Children generally think it's great fun to catch an adult telling a whopper.

I used to tell my children about Christopher Columbus. Everyone thought the world was flat. But Chris knew the truth and stuck with his beliefs and he was right. I told my kids don't believe something is true just because everyone else believes it. Investigate and find the truth in spite of everyone else.

An excellent example of my own parenting skills....
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Everyone alive should be taught critical thinking skills. Many people simply start out with pre-conceived ideas and this is not good enough.

Lively rhetoric.

I would suggest watching this video. Absolutely mazing advice for parents:

Soon they might be critical of your parenting! "What is the nature of my relationship with this lady? Who am I? Why should I analyze my own thoughts? Oh, what is the purpose of my life?" Critical thinking would accelerate an existential crisis in kids I guess

The Experiencial Learning model is perfect for this. Easily Googled. Basically, you create an activity, the kids do the activity, report what they did and what happened, they reflect on what they learned by doing/observing, and they think about how they can use the new knowledge. Think of it is: Activity > What? > So What? > Now what?

I reckon that youngster aged 7 or above occupy the limited amount of time they have for critical thinking on their siblings ,human nature being what it is . That is if they are lucky enough to have a sibling. Resentment against siblings usually lasts until they are all married off and that could be a long time.

How about asking them to list what bad points that their siblings would say about themselves ie get them to be self critical. Make it a competition for the longest list . Competition to be judged by Mum and Dad of course. Prize would be in multiples of weeks off rota duties. Extra points if your siblings do not mention a fault that you have yourself.

A single child family would have to be " make a list of all the faults you have EVER been told off about"

Talk to them. Ask them to support both sides of a given position. Get them to understand why people believe and not just teach them what they “must really “ mean which seems to common in discourse today.

Ask questions.

So, um, I wrote a lot. It's been on my mind for some time. You don't have to read it.

Recently, I've thought about how to best handle child development. My girlfriend has a 3 year old child and I endeavor to be a good role model and life guide. I think the ability to critically think well begins even before they have the capacity to think critically. That is to say, that there are things that can be taught about simple memory skills, behavior, sentence structure, etc.

What even is critical thinking? I looked it up and google said it's the ability to remain objective and judge only the evidence. It's still somewhat an unfulfilling definition. So, correct me if I'm wrong here, I think it's a little more than that. Applied critical thinking has something to do with the ability to come up with questions, answers, and everything in between that no one else sees, that people don't thoroughly consider, that takes into account otherwise unforeseen variables - this is the goal of critical thought. In short, it's the capacity to put two and two together - or take them apart - in a way no one saw coming and in a way that only takes into account evidence instead of the belief, the argument instead of the person, the concept AND execution, the implications of what is being said or claimed. Ipso facto: critical thinking isn't a skill, rather it is a collection of nuanced, yet rigid forms of consideration that can be applied in a moment's notice. Some people seem to do it at the drop of a hat, some people need to be in a certain mindset or need practice, some people struggle, some people have none at all, and some people never will. Even so, this isn't all that absolute. Perhaps more... ahem... critically, it is all the more precise to say that some people have some critical thinking skills at some points and when it comes to some subjects but not others.
Therefore, what can we do to germinate this possibility in our kids in such a way that "winds them up" and let's them at some point do it all on their own. For instance, how can we get them to think critically about, say, Legos and Marvel now in such a way that when they come across, say, a political dilemma and we're not there to hold their hand or give them the answers, they can still use these same processes.This is essentially a reiteration of your question.
So back to my girl's kid. Before critically thinking is even in my mind as a concept to espouse deliberately, I like to consider behavioral modification - i.e. discipline. My process for almost any time he is doing something wrong is: Tell him to stop politely and calmly, explain why he shouldn't do that, take him out of the situation, place a different option as to what he could be doing, offer yet another option if he doesn't like the first; if he continues to do it, I somewhat repeat the process, but threaten nonviolent punishment if he continues, but also immediately offer a small reward if he stops; if he stops doing it I offer encouragement and possible the promise of a reward for continuing this behavior. If he is doing something right or nice, I generally only offer rewards for doing or continuing, but no punishment for not doing. If he really gets unruly or continues his bad behavior throughout multiple days I threaten violence and I’ll slap him on the wrist - this is mostly when he himself is violent continuously. I'm still working on the process a bit. It doesn't work every time. I don’t always do it completely or at all. And who knows what the aftermath of this will be 15 years later.
My point with this is that if you just beat your kids and tell them no, they will only ever understand a rudimentary version of rules and behaviors and furthermore this may have consequences to their overall ability to think critically. I think things like these have a lot to do with the development of applicable critical thinking skills. I think we would all agree on an intuitive level that comparing a child taught more or less like mine will develop better methods of analyzing and evaluating things than a child who is just slapped on the first or second or even third time and never explained why. But the science isn't out yet (unless it is and someone can point me to a longitudinal study that uses this kind of comparison) and maybe slapping some kid will allow them to try and put two and two together as to why they got slapped in the first place. A lot of people "turn out fine."
This brings me to my next point about forcing the child to come to the right conclusion or to explain it to them. Throughout my high school and college career I noticed so many times that there seems to be an underlying pedagogical philosophy to not give away the answers. I remember once in art class, I tried doing a drawing of a toy duck in the center of class. I kept making his eyebrows look mean, and every time I tried to submit it to the teacher he told me that his face looked too mean and to go back and work on them. He was a nice dude, but I didn't know how to make the duck's face not look mean. I kept erasing the eyebrows and tried to redraw what I saw, but it didn't come out well. He never told me how to make it so I could draw nicer eyebrows. What angles should I do the lines? How should I hold the pencil? Is there a technique? What angles of eyebrows express which emotions? Now, perhaps he didn't actually know. Perhaps he neglected to tell me. Perhaps it was all deliberate to see if I would have a eureka moment. This is actually a terrible example because either possibility is just as likely. I notice the latter more often in English classes, mostly. So, assuming that his intent was to make me “get there,” I think he failed as a teacher at that moment. Basically, what I’m saying is that we often want to rend the “critical thought” out of someone, especially as a teaching device, but more often than not it doesn't come out. Don’t be afraid to give people the answers, sometimes, especially if they’re young and lack the previous knowledge: How can you expect them to put 4 and 4 together if they don’t know the answer to 2 plus 2? How can you expect them to put 2 and 2 together if they’ve never learned what 2 even is. More often than not, asking the class if they can give you examples of misogyny in the Odyssey works more to fish for those few geniuses than it does to elevate an already disinterested group of thirty odd people.
The next two sentences are two variations of the same idea I’m trying to convey. So, the main takeaway in this big wall of text is that the most concrete way to turn someone into a critical thinker, but by far not the only contributor, is to secure a pool and well of knowledge. So, the main takeaway in this big wall of text is that the most concrete way to turn someone into a critical thinker is to secure a pool and well of knowledge, but it is by far not the only contributor. Which is more correct and why? If you don’t know, then you don’t know. Anywho, what is the use of critical thinking if you have no knowledge to draw upon to assess claims and challenge incorrect notions and logic. You need to know logical structure before you can defeat it or whatever.
Now, there’s a lot of criticism on my part, but what solutions do I offer besides the tangentially relevant, possibly incorrect method of disciplining? More possibly incorrect things that I’ve never even tested on my own subjects (family children). Somebody test them for me.
First, paint mixing can be a satisfying learning experience. I’ll call it “guided paint mixing.” Basically, instead of letting your child go nuts with paint, which is also good sometimes, you sit down with them and explain how it works. “What are these colors?” You ask little Timmy.
They point them out, “Wed. Yewoh. Bleww.”
You then show them: “Watch what happens when we take some yellow and we take some blue and we mix them… What color is that?”
Some of them might be amazed, some of them might have seen it before. Let’s say Timmy is surprised. “Wow, it’s green.”
“Sometimes, when we mix colors, we get something entirely different from the first two things we started with… Now, what do you think is going to happen if we take some red and some blue?” You probe them lightly and say, “Do you think it’s going to be green again?”
If they say yes or no, ask them, “How do you know?” If they aren’t sure or don’t respond in a secure manner tell them, “You don’t know? It’s okay if you don’t know. It might be something cool.” That’s also an important and key thing, to allow them to recognize the depth of their knowledge. It’s important to challenge them lightly so as to make them unafraid of challenge in general; like, when someone challenges their beliefs or assumptions or outlook.
Maybe this could extend beyond paints to other small things where you see fit. Writing, math, storytelling, movies, etc.

I also think cooking is an amazing way to teach older children of ages 5 and up - obviously starting with light dishes. Teach them to follow the recipe and then teach them to break away from that convention. Test them after twenty or forty recipes by allowing them to make their own dish based on the knowledge they previously acquired - something entirely new.
And I think at this point you can get these ideas and run with them. Gardening is also a good one because it teaches delayed gratification. Certain kinds of video games as they get older can help, those like puzzle games and exploration games (Bejeweled, The Outer Wilds, Rime). Board games are also excellent (Rhino Hero, Checkers, Chess, Power Grid, any worker placement or resource management games). Establish the rules and look for setting up moments where they can ask, “OK, so if I can’t do this, but I can do that, does that mean I can do the other thing or not - where does that fall into the rules?” There are plenty of those moments in the board games I play with my cousin, which may be a little too advanced for kids below ten.
Listening to a variety of music or playing an instrument can also be a good activity. Perhaps read them increasingly complex stories or pieces of information and ask them to challenge that information. Ask them what they find wrong with it. Show them a red apple and ask this verbatim, “Is an apple green?” They’ll say that apples aren’t green. But then bang, challenge their assumptions by showing them a granny smith and say, “This apple isn’t green, but this one is.” Read them Mary Had a Little Lamb and ask them if they think all sheep are white, then show them some can be brown and some gray and some dirty. Sometimes, don’t give the answer right away, sometimes don’t give it at all.
There might be stuff I’m woefully missing, but the common thread in all of my suggestions is to expose them to things that are procedural and that lend themselves to questioning and experimenting. Not only that, but a lot of these are activities, not necessarily strategies, because activities are engaging for kids, they are structured and easy to understand - they’re not abstract. However, for a lot of parents, things like gardening can seem like chores, teaching kids how to cook can be a difficult task, and games can seem boring.
So the caveat I leave you with is to adapt my suggestions into activities, routines, or even just attitudes that you are more comfortable with - at least, in the beginning. Then, challenge yourself as well. Fuck that was rambly. I might spruce it up and submit it as an op-ed, I’m pretty proud of myself on this one.

Scooby-Do and the Wizard Of Oz, especially if you're around to help them connect the dots. Comparative religion, being exposed to all the mad variety of mythology people subscribe to. Used to be a wonderful show called "How'd They Do That", which revealed the secrets behind "magic" tricks. Learning to do "magic" tricks. Don't intervene immediately, allowing them to figure things out. Ask open-ended questions. Of course, expose them to and take time to explain the "nuts and bolts" (science or reasoning) behind phenomena and decisions.

Tell them they can't do something and watch the wheels work for them to do it.

I highly recommend my friend's book "Growing Up Godless." And I'm quoted in her final chapter (I'm LanceThruster online)! Has many insights from others in similar situations.

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"I see a pattern where the randomness of human actions can be directed through probability for an overall cumulative and positive effect. All throughout our society there is a butterfly effect that we are most always oblivious to… I guess my message is to go boldly forth and increase the peace and love and know you are not alone. You may not always be aware of the others choosing to follow this same path as you, but they’re out there, and they’re making a difference.”

~ LanceThruster

[from Debbie Mitchell's book "Growing Up Godless" - Sterling Publishing Co., Inc.]

Be able to be a devil's advocate & make the list. One side the pros, the other the cons. The debate. Learn to discuss without anger or violence or insults. We are trying to move the species forward sans warfare. Except for boxing & American football. Then after logic, emotion can express its feeling. And then sleep on it as our sleep mode sorts & strategizes . So old sayings are based in observing facts. It is how I train my dogs. =0}

Teach them logic, mathematics, the importance of questions...