No, they are not poisonous to the touch.......very few plants are. Consuming parts of the hydrangea is a different story but incidents of plant poisonings with children are relatively rare. Kids being kids, they tend to steer away from general vegetation and flowers and focus on interesting or appealing fruits and berries.

And it is important to understand that the vast majority of plants are toxic to some degree or another, even many common vegetables (tomato and potato foliage for example). It is the dosage that is critical and a good many poisonous plants taste bad enough that kids would never eat enough to harm themselves.

Just be aware of what the really dangerous plants are (your local children's hospital or pediatrician should have a list) and avoid them. And begin teaching your kids right away that nothing from outside goes in the mouth without mom or dad's OK first.

Folks have gardened for generations with small children without problems - use some common sense but don't make a big issue of it :-)