The plant will only cause a reaction if they handle the plant and then spend some time in the sun. The chemicals reduce the natural barriers to UV light that are present in the skin, essentially causing a sunburn to occur in a shorter period of time than normal. Are your children old enough that this can be explained to them? Given how robust cow parsnip is, it is pretty easy to identify and avoid but I can understand not wanting to take a chance if they are very young.

My children are 2 1/2 and 16 months old and we're adopting another infant in December so I'm afraid I have many more years of kids who won't be able to understand not to touch something. I love the plant but I'm afraid given all the research we'll have to take it out and replace it with something a bit more small kid friendly. Thanks for the feedback.

You could put a small fence arround the plants if you like the look. When your children are older you can remove the fence. A group of about 4 old doors painted wild colors by you and your oldest would corral the plant for now and if you could find on the street very cheap.