Don't forget 'The Princess and the Peanut' book - we read it to a group of young girls (Brownies, ages 7-9) last night and it went over very well - sparking lots of questions, compassion, and stories some girls chose to share about people they know who have environmental, food, and sting allergies. We have a food-free environment (except camps) and felt it was okay for girls to identify themselves as having allergies. We then proceeded with our lesson in first aid, including how to use an EpiPen and recognise an allergic reaction (hives, itchy mouth, breathing troubles, etc.) on top of the usual bloody noses, bandages, and bruises stuff.
I think proper education and awareness is important at every age. Outing a kid who may already feel excluded isn't appropriate, but teaching young kids what allergies are is important to them understanding allergies as they get older, especially if they have people with allergies in their class.