As the leader of a school gardening club, I thoroughly recommend this book to anyone who is worried about kids & poisonous plants (or even adults). (It doesn't cover pets though).
It lists 132 plants which are poisonous (one per page, with photos), how it's bad for you (what part of the body it harms), but puts the risk into perspective, such as "only a few cases reported".
It shows you there's no need to panic and remove all "poisonous" plants from your garden: sure, hellebores are poisonous, but actually who is going to try and eat one? Why would they? And they're no more poisonous than tulips, hyacinths & daffodils.
We all are taught that potato fruits are poisonous, and some schools are banned from growing them (really!) but actually there have been "very few" reported cases of poisoning, and ingestion is likely to give only "mild" poisoning with tummy ache which resolves itself.
Surprisingly, things like celery & parsnips are listed as potentially harmful (some people are sensitive to the sap and/or bristly hairs on certain plants) and of course some people are very sensitive to strawberries and peanuts.
Interestingly, many many more adults are poisoned than children, because they might eat a big batch of foxglove or comfrey leaf thinking its spinach or they make a herbal tea from something unsafe. Kids go for berries, which tend to be bitter and get spat out. As someone said to me recently "my children won't eat ANYTHING green unless it's smothered in ketchup".
There's a useful first aid page near the front of the book, which I've typed out for the First Aiders in our school.
I feel very relieved now, confident and well-armed against the panickers :) Worth every penny, and I think every school & town library should have a copy.