The Short and Dangerous Life of Toads (and other small creatures)

We have had many garden toads hopping about our flowerbeds and living in our stone wall this summer. Julia loves them. She loves all sorts of little creeping and crawling and hopping creatures. Lightning bugs, frogs, dragonflies, caterpillars, grasshoppers, minnows, crayfish, anything. (No snakes yet. Hopefully she will never take a liking to them and start dragging them into my house.) Unfortunately, she often loves the little buggers to death. She will let the little kids carry them around until they've been dropped one too many times. Or maybe she will fill a jar with water and minnows and/or frogs and then leave it in the sun to boil them to death. I've always been bothered by kids doing that sort of thing. I don't know what to do. I don't want to discourage her from exploring nature, and even being able to observe it close up for a while. But I'm trying to teach her the catch and release approach. Maybe a time limit? You can keep a creature for fifteen minutes? I'm not sure what the answer is. As I'm trying to figure that out, all small creatures beware.