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These are herbal preparation,hence there ingredients are not exactly known. Their effect on immunity is questionable hence we can not comment on those preparations.
I would suggest you to consult a Paediatrician to examine them and if there is anything is there proper supplementation can be given.
You should take care of their normal diet if weight gain is required proper protein and vitamins
may be given by the doctor .
To gain weight apart from diet they need to play( Exercise).
Hope this information helps you.
Dr.Akhilesh Dubey M.D.