Is your son allergic (Celiac Spruce) or does he have a sensativity? Also is he allergic to everything else or is it a preference?
I ask because my mom has Celiac Spruce & doesn't eat beef by choice. She also has COPD & her meds cause her blood pressure & sugar to rise. This limits her even more. My daughter doesn't have a problem with any food but doesn't gain weight easily. I give her a lot of avacodo, & put AnnaMarie's Organic Olive Oil in everything I can to add calories. The reason for this brand is I know Anna Marie personally and know how her farm is cared for. She flies to Portugal & overseas a large portion of the process to make sure it's done right, it's third generation organic, and believe it or not the nutrtional value is different. Although she only brings in almonds for personal friends they also have a different nutritional value then those in this country. They are extremely expensive, most people in Portugal buy almonds imported from California. If you go into any grocery store and look at the difference between the nutrients in regular almonds and the raw organic ones $6.99 a pound versus $18.99 a pound but worth every penny. The almonds like the oil also have nutritional values that are superior that are not listed and almost medicinal.
There are web sites for Celiac's and also you might want to go see a nutritionist just to be on the safe side. My cousin who was a vegan by choice. His son became ill & their doctor ordered them to add eggs & fish to his diet, they later added meat. Since he is so young you have to make sure that what he eats is enough to meet his nutritional needs so that developmental issues don't occur. I don't want to scare you but mistakes made now can cause life long problems.
I hope this gives you a few places to look for more in depth information. Best of luck.
Kim