Another point to consider: most people (even trained dieticians) don't know
all the milk "ingredients," such as casein or even whey.
My 5-year-old (anaphylactic milk allergy) is in preschool and I always provide
his lunch and snacks. He'll be entering kindergarten in the fall and we've
already arranged that I will continue do just that.
He knows not to eat anything unless his Mom or Dad reads the ingredients
first.
And I know (from prior mistakes) that you can't expect anyone else to know
everything we need to know to keep him safe. Also, I can't expect someone else
to be as ever-vigilant as we have to be.

It has just become part of life as we know it. It can be stressful at times,
but he recognizes that this keeps him safe and healthy and, therefore, happy.
Most of the time, he doesn't even mind.
And when he does ask if he'll always be allergic to milk, we tell him the
truth: We don't know. But if he is, he'll know how to keep himself safe as he
gets older!