> socialization, friends

This still happen at daycare. If you have sent your kid to daycare/preschool, you'll know that kids become friends wit nother kids there, and parents can become friends withnother parents. A community forms because playdates are necessary when daycare/preschool is out.

> parents

Sometimes economic realities are such that both parents have to work to make ends meet. There are single-family households that also exist. Childcare is a necessity in these and other situations.