I often brush my son's teeth twice per day. he is 2 years old, no sugar food but his teeth have a lot of black stains. what should i do?

See a dentist: Bottle carries (cavities) are sadly common in toddlers. Generally caused by a combination of things: being kept on the bottle beyond the first year. Giving juice via the bottle. Allowing children to walk around, lay down and chew on their bottles leads to bad tooth decay.

Sugar: Sugar is too often where we don't expect it. I have seen non caries stains from vitamin drops not diluted, particularly iron. Also several non diluteded fruit juices cause tough to remove stains. Hope that helps.