Hi I am Dr.kadhir, I can understand the current situation but it would difficult to comment on it without knowing his general condition and is also important to know the quantity of black vomitus . It can be due to any recent intake of drugs of dark color or blood. Blood can come from vomit as red, brown streaks or black color in case of old clots . vomiting blood may be caused by swallowed blood, as from a nosebleed or forceful coughing which is common due to cold and sore throat. But bleeding can also come from stomach due to increased bleeding tendency or ulcer.It can be something more serious and needs immediate medical attention. I can reassure you if the child is better clinically and the source of bleed would be from local sites like throat or nose . But at same time if the child has fever , rash or bleeding spots over the body (petechiae) or if he looks dehydrated and sick then he needs immediate medical attention. Thank you for the consultation in health care magic.