My BB had Brown Rice since she was 5 months old ...she had 3 boxes...then we started Oat meal...I didn't realize the sequence was wrong. But, my BB had skin sensitive when she started the Oatmeal. I brought her to doctor...took so medicine...then she is recovered. I let her try Oatmeal again...she loves it..then we continue and this is her 3rd box of oatmeal now.
as long as you give your BB one bowl of cereal and your BB won't cries for milk earlier than usual, then it can replace one meal of milk. Also, you can use milk to milk cereal, it gives your BB more nutruients.
I called Healthy times but the staff actually told me Brown rice is the one to start first (because it is RICE), then oatmeal (which many BB loves it cos it is quite sweet) and then barley (which COULD be allergy to BB) and finally mixed. Once oyur BB can take all three (Rice, Oatmeal and Barley), then you should always serve your BB with Mixed cereal because it contains different type of cereal and gives BB different nutrients.
Always start with very little first. e.g. 1-2 tbsp. once your BB takes it happily, you can continue to add until it mix into one bowl.
Poo Poo should be not be affected by eating cereal (although at the very beginning, there might be some changes to your BB's poo poo as he/she is getting used to taking solid). Give your BB more water, or try not to mix the cereal too thick could help if po po is hard. My BB has very nice poo poo ever since I order cereal. Add vegetable paste (solid) once your BB can take the cereal could help his/her Poo poo
if your BB is 100% breastfeed, then 6 mths, however, if you are already serve him/her formula, you can give your BB starting as early as 4 mths. This is what my doctor told me.
if already offer a lot of water, you can try to "massage her tummy". However, i dont think it is due to eating cereal. maybe give her vegetables as well can help