“What causes chest pain in children?”

Too broad a question. Not enough clinical data.

Chest pain in younger children is usually not serious. Most of the time it is chest wall pain or occasionally related to reflux or heartburn. Rarely is there a cardiac issue. Chest pain with exercise or associated with passing out (sycope) can be more serious and should be evaluated. Most primary care providers are good at distinguishing a serious issue from one that is likely benign. They can then help decide if it needs referral to a cardiologist.