There are ways.

One, parental control software on whatever device he is allowed to use.

Two, Change the DNS servers on your home router to ones that can control which sites are available. Opendns.com is really good and configurable to block or not block things, ranging from porn to known phishing sites, as well as time-wasters like social media. If DNS can't (or won't) resolve to go to those sites, you can't connect to them. To mitigate this on your own devices, set the DNS servers on them to be able to bypass the limitations. Alternatively, hard code the DNS on the devices, but some are locked enough that you can't if it is using cellular data. All of that is pretty easy, though it sounds techy.

Three. I have a tech contract with my kid. It lays out the rules and boundaries as well as the consequences for crossing them. I have grounded him from the devices for minor infractions or completely taken them away permanently for major infractions.

It works. Parents, teachers and the local police love it. PM me and I will send you a link to download an editable copy.

As kids, I think most of us made a point to try to see things we were forbidden to see. The forbidden only encourages curiosity. let's fce it mos tof Facebook is pretty much no worse than what you se on TV.

I think it is better to just be frank and honest about internet predators and to answer all questions a best as you can, includign saying "I don't know" if you dont' know something.

If your only rason for forbidding somethign is "because i said so" or "because you are too young" without explaining why soemthign is age loimited, the kid won't really listen. Tell them why it is forbidden with legitimate reasoning and kids will for the most part do the righ thing.

Some good suggestions here, and I can speak franky and say if had seen some of what's out there as a teen I would probably have issues today. Or I would have died from complications caused by excessive masturbation (if there is such a thing)! The thing to remember, if they want to see it they will find a way, if not at home at a freinds house.

OK
easiest way for me, if it is a windows compute, though it does work with others
create a "hosts" file.
In Windows 10 it is stored at C:\Windows\System32\drivers\etc\hosts file
you can search for it.
open it in note pad and edit it,
just add the name of the site you want to block and give it an address,

ie 127.0.0.1 website url etc

whenever they try and go to that site, the get redirected back to their own computer,
you could go one stap further and create an index.html file with some code that says "I have told you not to go to this site!" and save it in the root directory of the computer.
You need administrator rights to do this.

This is what I did about 15 years ago when I had teens in the house, I just checked, it still works.
here are some instructions.
[support.rackspace.com]

Kids have to know thouse things, that's the world they are living in. I did that with my two daughters. I never wanted them to fall behind anything. This world is too competitive as it is. The only thing I enforced and it was not negotiable, they were not allowed to shut the door while on line and they never had a computer in their room. Today is a bit more difficult to enforce with smart phones.... Its a thin line....

You can create a restrictive list by labeling it as an untrusted site. There are parental filters on tablets android especially for children under 14 allowing you to enforce limits like hours it locks them out, which apps are allowed and toggle camera features and mics off and on. It's called family link. And it is a google app.

You don't.

Remember way back when you were young... or your friends... what was the average response to "whatever you do, do NOT do..."? I recall that most of us kids DID exactly that.

So, don't make it taboo, just give guidance on how to do it safely. Give knowledge and critical thinking skills. Teach them to question motivations and to understand why things are happening (as well as how) on the web, and in their life... this sort of reasoning is missing from the religious right and no small reason why I prefer the agnostic/atheist side of life.

Set the parental control on the computer, and password protect it to ensure that children can't access inappropriate sites when you are not there.

If the only way they can access the net at home is through wifi unplug the router when you can't closely supervise the child's web use.

No access to a computer when parents aren't home. I kept the computer in the living room or my bedroom with a 2 hour daily limit including homework. This was in middle and higj school.if he chose to play for 2 hours, the computer was unavailable for homework.

Well the thing is to remember that he is a little kid. Too often we forget that children, although they may talk like little adults, are actually, very undeveloped minds.