I don't know about anyone else or how they handle child situations but with my first exh (we have a great D relationship) we each have first right of refusal. If something comes up then I call him first and ask if he can take the kids, if he cannot then its up to me to find alternate childcare. He does the same for me. I want to be asked first to take the kids. Why would you (or they) want to be with someone else besides a parent if it was at all possible?
Me: 46 FWS: 36 Married and Divorced 4/07, Pregnant 7/07,False R 7/07 Baby Girl born 3/08 Kicked him out because OW: 7/08 5/10 He realized what he had and lost. Moved home! REMARRIED 3/14/11!!