J.B.
Believe it or not- my daughter cannot have chocolate either! In her case, she gets stomach cramps and vomits violently!! My mother also didn't believe me and gave her some chocolate at a restaurant one evening when we were all out to dinner and my daughter became soooo ill!! She didn't vomit, but she might as well have!!
I found out that it's something in the cocoa that causes the reaction. My daughter can eat white chocolate, no problem. And I also found out that chocolate or cocoa allergy is pretty common among children- but that most of them don't outgrow it. It's a lifelong issue.
If you want to know for sure, have your children tested by an allergist. And ask them to do a scratch test for cocoa powder, cocoa butter and chocolate liquor. I've been meaning to do that with my daughter, but for now we've just been avoiding chocolate altogether.
And make sure you tell your childcare provider, teachers, friends, neighbors etc. Because you never know when a situtation might arise where your children are offered some cookies, cake or candy with chocolate in it!!