Yikes! I'm so sorry you are having to deal with that. The surprise element (when you think you are serving perfectly safe food) is just awful, isn't it?

Just in case you're not already plugged in, you might also connect with people at Kids With Food Allergies: http://community.kidswithfoodallergies.org/pages/community

Joining is free, and there are some extremely kind people there who have been through what you are experiencing.