@ what age does DHA need 2 be introduced into child's diet? He is 4 months old. Also his feet & hands a little purple, is this bcause he is cold?

Unknown. Dha is an omega-3 fatty acid important for developing babies and children, so it is good to have some dha intake, either from breastmilk, formula, and/or foods. The problem is that it is not known how to tell if a baby has too little or too much dha, how much is needed, how much to give, nor how digestible or absorbable various dha brands are. Talking with a pediatrician can help with the details.