What is cause of chest pain in child?

Many. Chest pain most commonly is musculoskeletal in children (it comes from the muscles and bones of the chest). It can also be caused by gastroesophageal reflux (heartburn), pleurisy (pain from the lining of the lungs, usually from infection), or, less commonly, from the heart of large blood vessels. If the pain involves fever, weakness, or difficulty breathing, medical help should be obtained.
Many things. Many things can cause chest pain in a child, and any chest pain should be evaluated by the pediatrician.