A top belay necessitates having access to and egress from the climb, and is essentially free climbing in nearly its purest sense. The key to any toprope anchor is the object it's attached to. If you use bolts, make sure the nuts are not rusted or loose. If you use a rock or tree, they should not be hollow-sounding or loose. What I do while climbing with my partner is another game I'm supposed to know what I'm doing and be responsible for doing it.
Children depend wholly on the correctness of their parent's judgment for their safety.
There is a simple test to give an anchor to determine whether it's rigged correctly and safely. If you took an imaginary knife and please note, I said imaginary and cut one of the slings, runners, or whatever you're using to hold the biners that are holding your climbing rope, and the rope would fall or move from its position because of this one failure, the anchor is not set safely, it isn't bombproof. For the sake of illustration we'll return to the live tree at my children's first toprope site as an ideal anchor point. Take one of those runners you purchased, or so lovingly tied, and loop it around the tree. Take another runner and join it to the first.