Its seems unfair to take a child to an event and then not let her fully participate in it unless there are allergies or something, in which case provide an acceptable alternative and a fair warning of what to expect. If you are that worried about food additives, I would avoid such events.
I am not a fan of additives either, but I try to consider the health of the whole child. Taking her candy might be better for her body but worse for her heart. And I have seen first hand as a teacher that restricted kids totally pig out on their candy. One litte boy ate almost his whole bag of valentine treats before his mom arrived. I didn't even have a chance to stop him before he popped like 5 candy bars in his mouth. Little kids are smart, they know how to work the system.
