Hi Minnu,
I want to add that sometimes thal minors can also be iron deficient, so if the doctor suspects this, a group of blood tests called iron studies should be done to see if he is iron deficient before taking any iron supplements. At his age it can be hard to get him to eat fruits and vegetables but try to find some that he likes and will eat. Chewable vitamin C tablets might help reduce the amount of colds he gets.