It has been theorized that children with imaginary friends may develop language skills and retain knowledge faster than children without them, which may be because these children get more linguistic practice than their peers as a result of carrying out "conversations" with their imaginary friends.[11
Imaginary friends are an integral part of many children's lives. They provide comfort in times of stress, companionship when they're lonely, someone to boss around when they feel powerless, and someone to blame for the broken lamp in the living room. Most important, an imaginary companion is a tool young children use to help them make sense of the adult world.[12]
I would hope this child has some actual friends as well.