We asked some friends of ours who also have a child to Sunday lunch (without kids). She has parents and family around and friends who sometimes look after her boy, so I didn't think a babysitter would be a problem.
We have a new babysitter, who just started this week. The first time she will be looking after both our kids is this Sunday and she is a bit apprehensive, though I think she is quite capable.
However, my friend can't get a babysitter and has asked if our babysitter can watch her son also. I feel uncomfortable about asking my babysitter to watch 3 kids, two of whom she's never looked after before. I've told my friend this, but she's making me feel bad about it.