It’s about the children too
Most parents think about babysitting co-ops from their point of view (cheap babysitting). While reading this post I was reminded of something my aunt once told me about how all of the children in their co-op were friends and continued to be friends long after they were old enough to look after themselves.
Even if you don’t need a co-op it might be worth joining one just to help your children meet some new friends. There’s more to be gained than just cheap babysitting.