I quote from her article The Vital Role of Play in Early Childhood Education:
"The way children engage in social play with others changes over the years. The one year old tends to play alone, while social play of two year-olds is generally called parallel play for young children play side by side without fully interacting with each other. I would characterize the play of three and four year olds as playmate play. The children enjoy playing with each other (with occasional squabbles as part of the play experience), but generally they are not deeply invested in each other. They enjoy playing together when they are in nursery school, but tend to forget about each other when they are apart. An exception to this, in my experience, occurs among children whose families are friends or who carpool together. In such situations, life thrusts the children together outside the usual play times, and playmates become more like family members who play an important, abiding role in a child’s life. Normally, however, children of this age happily play with their playmates in school and forget about them for the rest of the day.
The social play of five and six year olds is different. The doors to deeper social relationships are opening for them. They form friendships and talk about their friends at home. They think about their friends when they are apart. They may want to call them on the phone or visit in their homes."
H is turning 5 so I guess he's starting to display the social characteristics of a 5 year old. It's rather sad that we have to pull him out of school at the end of this semester now that he has formed firm friendship in school. He actually wanted to stay in his current school but that's another story altogether.