Two sources you might check are your Poison Control Center and the local cooperative extension office. Both should have some lists of toxic plants.

Here's a listing that should be helpful. A note of warning - this list is huge! Many more plants are toxic to some degree or another than those that are not, including many common vegetables. But toxicity varies considerably and the highest degrees of toxicity are generally associated with ingesting or eating part of the plant. Most kids of preschool age and older can be easily educated to avoid putting non-parent approved plants or fruit into their mouths, but it is always best to avoid those that produce enticing berries or seed pods or those like oleander, whose toxicity is very high.

And many children (adults, too) will experience dermatitis or phytosensitive reactions to some plants. My daughter developed huge welts from contact with common rue, Ruta graveolens, that lasted for weeks.

Here is a link that might be useful: toxic plant listing

Gardengal,
That's exactly what I was after. UC Davis should be a good resource. I know some people are sensitive to plants that are considered harmless, so I feel I need to be sure to have the most innocuous plants available.

We talk with the children about eating plant parts (carrots, lettuce, etc.), but the kids know they cannot just go outside and eat any plant. Thanks for the reminder on that though. And thanks too for the website.

Hi all
many plants listed as poisness plants are also have been used as medicine in Japan and China for centurys.
Understand each plants and know how to use it is key.
Mordan medicine can save live of many human but if not use correctly medicine can kill a person. Plants /tree are same
yama

Hi all
mango, lemon,lime,potato,popy, prune,persimon,tabaco should be listed as poison plant too.............yama