I thought I would share a little about our non allergic child, from the perspective of being the younger child, of a sister with a milk allergy. From an early age she grasped the concept of cross contamination, and hidden milk.
When she was in kindergarten she would eat her cheese, wash her hands then eat her fruit, even with out big sister in the class, for her it was a habit that she wanted to keep.
She came home from a play date more recently, and explained that she had something with milk in it, but it was very clearly labeled. She has decided that she will avoid eating things with hidden milk, in support of clear allergen labelling in Canada, even at other peoples houses. She came up with protest on her own!
We make a point of taking her out (about once a month) usually to a mall food court, or ice cream shop for a treat, without big sister.
It wasn't till recently we took our non allergic child to a buffet restaurant. During our main coarse we talked about the ice cream bar. According to her this was the best part.