First of all please please do not be enslaved by glamorous advertisement which tempt you to buy over the counter products.
To increase in immunity of your child please try to suggested weight which I think is printed on Immunizations
records of your child. Maintain suggested weight Keep check your child increase in height by every on an average of 5-6 CMS every year
For good heights and weights give fresh prepared with love of mothers at home which your child need to grow spiritually stronger.
And a very difficult task never give your child chocolate or sweet at night.
Further you can consult me or any homoeopathic doctor to give you medicine to make sure your child immunity is maintained by homoeopathic medicine.
Hopefully your questions is answered.