Is it true that flax seed oil or omega-3 fats will help a child with add?

Generally No. The benefits shown in research are minimal at best.Not worth the money! altho more research would be helpful.
Omega 3 and ADD. Flax seed oil does have omega 3. Omega 3 in several studies does improve some add symptoms but are usually not enough of an effect to overcome the issues children have with add. But I do reccommend it with my add patients along with other medicines.