Everyone is different and need different things. Introverts need time alone to refuel their tank, extraverts need time with people to refuel their tank, one is no more right than the other - it's relative.

No, I don't think you need to send your kid to childcare in order for them to be "socialised", and it isn't something they have to spend huge chunks of time doing in order to be "socialised". Being socialised basically means that someone has learned how to get along with other people. No where do I see that as meaning only being able to get along with people in your same peer group, and generally speaking people from similar socio-economic groups tend to congregate in the same area, go to the same schools/child care etc. so going to these places doesn't always mean that a child will experience diversity. All that means is they have learned how to get along with that particular peer group, and that doesn't necessarily make them really socialised. People need to be able to get along with those younger, older, black, white, and everything in between. Every person a child interacts with will "socialise" them, including you, siblings, grandparents, cousins, the guy at the counter in the shop, kids at the park, the boy next door. It doesn't have to be large groups of same age children.