I am probably going to get in trouble for this post. I have been a member of a large congregation and the member of a small congregation. It is much easier to handle it in a small congregation. You still need to monitor who your child is hanging out with. I know what you're thinking- this is church! Well you would be surprised what "church kids" will do. Learn to tell your child no about these kids too. And I know that you are supposed to be able to trust the adults at the church too but I know that you have seen the news to know you have to be careful. I am very fortunate to not have to worry about these things where we go to church. I would trust any of the adults with my children no questions asked. (I have run out of the church with a hurt child and never even worried about my 7 month old child sitting in his high chair. Yep just left him never even thought about whether he would be okay or not because I knew he was.) I don't question my children's safety with any of these members of our family. We are lucky in that regard. But sometimes there are church activities that your kids just can't go to because of expense and you need to learn to say no and be honest with your children as to why. These are also church activities that may not be an "approved" activity for your family on a normal every day basis. And you need to go ahead and teach your children that just because it is church does not always make it okay. There is even times where the amount of activities is becoming so overwhelming that there is no family time in there. This is another situation where you need to help your children learn to say no and learn to balance their activities.
Just because it is church does not mean that it is necessarily always a yes.