I'm sorry for your loss.
I only let 3 children near my tanks. They are my cousin's kids, ranging from 3-8 years old. They know well enough that if they want to see better I'll find a step stool or lift them up. They know that if they want to see the fish fed, they can ask me, and they don't get upset if I tell them "No, I've already fed them today." The first thing I taught them was that they shouldn't hit the glass, and aside from the youngest they listen. The 3 year old I think gets it, but she's 3, so she might just be doing what her older brother and sister are doing. I don't really care why she behaves, so long as she does.
Their parents did an excellent job of teaching them to respect other people's stuff, that live animals are not toys, and that they should listen to adults. They know if they don't respect my rules mommy and daddy will not be happy. Mommy and daddy know roughly how much money I've spent on the hobby and they know that I own some rare/expensive fish.