At how many mths did u start ur baby on cereal & how do u clean their tongue thats white because of the milk?

my son ate between 2-4 oz. every 2 hrs until he was about 8 months old. i started him on cereal around 14 wks old, but i dont think ur supposed to be giving her alot of water that can drowned her kidneys they use to give babys water but now they say its bad.