My one brother & his wife don't have kids either, instead they "rent" kids from various parents when there's a particular "kid oriented" something they want to do. The first round of rent-a-kids is now grown up & having children so instead of merely being the Uncle & Aunt for the afternoon they now get to be alternative set of grandparents for the afternoon.

This works well for them, they were, in fact, trying to sell us on the idea. (The nice thing is they would "rent" the kid at prevailing babysitting price & so everybody got to have fun & no extra money ever had to change hands.)