I just found out today that my little baby nephew (19 mos) is allergic to eggs, milk, wheat, and peanuts (at the very least...that was all they checked for in his blood so far, I believe). Man! I can't imagine how hard that diet is going to be. He's had terrible eczema all his little life and recently started breaking out in hives due to peanuts....so they got his blood checked and wow.
Anyway....would like to start looking into mail-able cookie (or whatever) recipes (they live long distance) so I can send him treats or at least share the recipes with my sister.
I guess they'd have to be gluten-free or made with rice flour or something? And then no milk or eggs...yikes.... can you substitute rice flour for regular flour evenly?
You can use Kosher Pareve margarine and rice milk to make a buttercream. Anything marked 'Pareve' is guaranteed to not even have a trace of milk in it (the rabbis take this *extremely* seriously).
I made one last year and everyone at the party couldn't believe that my icing had no dairy.
There is an egg substitute available for baking. I'm not sure about wheat substitutes as I've never dealt with that allergy.
Keep in mind though that anything prepared in your kitchen may contain traces of allergens. I have a severe nut allergy and while I will happily bake for anyone with a nut allergy because my kitchen is completely nut free, I would not bake for anyone allergic to eggs, milk, or wheat because all of my equipment has come into contact with those allergens.
The dairy-free buttercream I prepared last year was for dietary restrictions, not an allergic person.
I guess you'll have to find out how sensitive your nephew is to his particular allergens.
Good luck! HTH!