Updated: Jul 23
Although it may look like babies or small children are sort of playing together, they're actually not what they're doing is something called parallel play. So they will play next to a child, but they're not actually actively engaging with them. By the time they get to around about 18 months of age, a lot of them are ready developmentally to start exchanging items and toys with other children. Not always nicely, I have to say sometimes they will just grab what they want.