C.T.
American pediatricians are the only doctors in the world to say it's OK to start solids at 4 months. In every other country they have done extensive research proving their digestive systems cannot break down complex carbohydrates (any type of cereal) until after 6 months - many countries even say 8-9 months and start with fruit and veggies at 6 months only if they have teeth. If you do choose to do cereal this early mix with breastmilk or formula since that should be the most of their nutrition, water would be giving them empty calories (the cereal) with no nutritional value. I wouldn't introduce fruits and veggies until 6 months atleast.