Certainly, it is not evolutionarily normal for children to spend the majority of their time immersed in a peer group composed of people within a year of their own age. Nor is it probably healthy. Children act rather like animals when they’re in groups together. Not only the immaturity of adolescence, but the barbaric cruelty of much of it, may be due to the fact that herding children into a series of age-segregated activities profoundly retards the process of socialisation. If Judith Harris is right, and peer group effects dominate parental influence, we are in effect letting large groups of children raise each other.
Find Judith Harris. Buy me her book.