My baby is 4 months and 3weeks. She had her 4 month check up already. So it is up to me when to start her on rice cereal. How do you know when they are ready? She has really been watching me eat lately-like she wants some. She is a formula baby...My milk supply was too low. She is a little peanut-she weighs 13.1 pounds. she was little when she was born-6 pounds. She is growing good my Dr. says. I was thinking about starting her in a couple of weeks? When did you decide?