Fortunate toddlers do go to school. Lots of babies and toddlers only get interaction with other children in daycare, which I assume provides some developmental benefit.
Yes, it was a tangent, but just wanted to point out that, for many in the US at least, it is not like decades ago when kids were out playing in the neighborhood. It is very possible that most, if not all, social interaction between kids happens in daycare, school, gym classes, or otherwise supervised get togethers.