For kids broken sculpture in clay, I prefer silicone glues. THey are a
bit flexible, and not brittle like epoxy. They are waterproof and
permanent. If you knock the broken area, it is not as likely to snap
off again as if it were fixed with epoxy. Clean up extra glue that
squeezes out right away with paper towel, but later, if there is still
glue to clean up, use lacquer thinner on a q-tip.