When can u start giving baby rice cereal?

Started my son on Multigrain cereal at 3.5 months every other bottle only at day care. He rarely gets cereal at home because i don't bottle feed him at home.

My bby girl was eating every 30 min so I gave her cereal at like 2 months.

Our doctor said to skip rice cereal because it can cause problems and isn't nutritional at all. We did oatmeal instead from just after 4 months. He was trying to eat all our food and could sit on his own so the doctor said to give it a try.