Pieris is toxic if eaten - but an awful lot of plants and shrubs are, as well - far too many to list here.

My feeling is that children need to be educated not to touch or eat any plants or berries in a garden. If they're very young children, they wouldn't be out there without adults anyway, would they?

Agree with Spritz - its an important part of children's education to not eat or chew leaves of plants - over 50% of common plants grown here are toxic to some degree if ingested. That said, having had kids myself, I have to say I never once saw them attempt to eat leaves or stems - berries yes, leaves no.

As a child, I learned very early that oleanders were "icky", and cacti were "poky". I would give your kids credit for a learning curve, supervise them when they are very small, and save the serious worry for other hazards.