It is no surprise to mothers and fathers. When you live with young children you know how the pace of their life picks up, how their tone and spirit are better when they have friends. That sounds simple but it is a basic contribution. Do not make light of this. Finding a friend, working with a friend, keeping a friend are fundamental life-jobs.
Children have to get the hang of working with others.
Learning how to get along is a stormy path. Young children need friends their own size and their own age. And young children like that. They like to know where they stand. Discipline doesn't stick out the way it does in an upper school, but the discipline is there.