I disagree wholeheartedly with all the advice given here. I'm sorry, but I do.
When you introduce cereals and such to your babies too early, you're putting them at higher risk for diabetes.
Also, about them not being "satisfied"... More often than not, giving cereal to a baby that young is more of a hinderance than a help. Their little digestive systems are not yet capable of handling the texture, much less their motor skills to swallow it. All the nutrients a baby that young needs is in breastmilk or a sufficient formula. If you start solids that early, they aren't getting the necessary and needed milkfat (in proper quantities) that they need for brain development.
I can't believe what I read here.