The causes of black stools in babies include physiological factors, such as food intake, while they may also be caused by pathologic factors, such as gastrointestinal bleeding. 1. Physiological factors: if the baby consumes certain dark-colored foods, such as animal blood, liver, or after taking iron supplements, the stool can also be black, as long as you stop taking them for a period of time, the color of the stool will return to normal. 2. Gastrointestinal bleeding: due to certain reasons, babies have gastrointestinal bleeding, which can be manifested as vomiting blood, black stools, and the stools can be tarry, when the amount of bleeding is large, the feces can be dark red or even bright red, and it is usually accompanied by dizziness and fatigue and other symptoms. There are other causes of black stools in babies, so it is recommended to take your baby to the hospital for a checkup to determine the cause and then give him/her the appropriate treatment.