I found my old allergy free cake recipe. This is what I made for DS for birthdays for years, iced with applesauce, poor thing.
2 c. flour
1 c. brown sugar
3 t. baking powder
1/4 c. applesauce
1 1/3 c. water
1 t. vanilla
Bake at 375 for 30 minutes
To make it more Thanksgiving-like you could substitute pumpkin puree for the applesauce and then add some allspice and nutmeg. In place of water, to make it richer, you could add a milk substitute like rice milk.
Something that might be fun is to make the cake into little whoopie pies. Marshmallows are actually pretty allergy-free, so you could use the fluff as filling for the pies. The only problem I've ever had with doing that is that the fluff can disappear into the cakes after a while, so you'd want to do it just before Thanksgiving to avoid the problem. Kids love anything with marshmallow, so I'm sure that would be a hit!
Another idea for something less dessert-like, but still sweet would be a traditional sweet potato casserole. The marshmallow on top is allergy-free, but sweet, so the kids might like that.
ETA - If you'd rather do something like a pie, let me know. I've done crustless pumpkin pies for DS before and they've turned out great!
Re: **holly321**
I don't know how she is doing it with the coconut allergy. I would be lost if I couldn't use coconut oil to bake with!
I will add your nephew to my prayers. Food allergies stink, and then to have asthma on top of it. That stinks