Is it possible for a child/teen to have a heart attack?

Rare but possible. Acute myocardial infarction is rare in childhood and adolescence. Children and teens can have a heart attack due to either an inflammatory condition of the coronary arteries or an anomalous origin of the left coronary artery. thrombotic coronary artery occlusion from kawasaki disease may occur in early childhood.
Drug use. I agree with dr. Kim- it is rare for children to have heart attacks. Cocaine and some other drugs that affect your vasculature may cause heart attacks in children who use them. Just another reason to say no to drugs!
Generally no. Children are at very low risk for heart disease and heart attacks. But if they have congenital heart disease, they are at risk for other illness related to the heart, such as heart failure.