I had a situation a while back where an adult (with no allergy experience) told my child that her cookies where milk free. My child said "no thank you" and continued on her way. The adult insisted, and was insulted that I did not trust her.
She then became more persistent, trying to convince my child (in front of me) that her cookies where milk free. As I became increasingly annoyed, my child slipped out into the hallway where I meet her, and we made our exit. With a line up behind me and her attitude, it was not the time to educate.
We already decided to go to this event, leave at the end, not staying for snacks and coffee period. The plan was then to go to the health food store, to pick up some organic produce and Organic Works Cookies that are dairy nut and egg free. We had the situation under control in a way that works for us.
Organic Works does use milk in the factory but they use different equipment and are very allergy aware.