It depends how much flaxseed is given to them daily. If it's only flaxseed bread in the morning or crackers as afternoon snacks, it should be ok for every day eating. But if you give tablespoon fulls to them for therapeutic use, I'm afriad that I do not know the answer. So far, all studies on flaxseed, ALA and heart conditions have used adult only (not children or teenagers) as subjects.
http://www.healthcastle.com/flaxseed_vs_flaxseedoil.shtml