i personally felt 4 month is a bit too early to start on white rice. my boy is 6kg at that age. the nurses who check on him find him a bit small but asked wether my hubby is small built. (im small built myself). and i said yes. sometimes its due to the genes. i only started him on baby rice when he reach close to 5mths by adding a bit of the rice porridge in his milk. but must make sure its soluble enuf to go thru the feeding bottle.