Babysitting exchange

Ok, I'm a little confused as to how this would work. In theory, this would be open to any mom in church, yes? But let's say that I'm not comfortable leaving my kid with Mom X. Mom X, however, is entirely comfortable leaving her kid with me. What happens then? Also, if we're all in a point system, how do you know who it's ok to redeem your points with? For example, what if we all really like the way Mom Y babysits kids. So I babysit Moms A, B, and C's kids, rack up a bunch of points, and then redeem them with Mom Y?

I'm probably just completely missing the point. ;) Can someone help me out here?