personally i would prefer to wait till 6mths old then start, no harm starting late. if start too early we not sure if baby organs can take it or not, esp the liver. and outside made cereals, no matter how little, sure have additives etc in it. so home made porridge is always preferred . but if really busy then bo bian, use instant cereal is ok. brown rice maybe can wait till baby is 8mths coz i heard brown rice can cause indigestion easier than normal rice cereal.