Hi thanks for contacting HCM... Noted your child having blunt trauma to chest wall.... It could be ...... -rib facture -muscular strain. -costochondritis that is inflammation to costal cartilage Rest is needed to your child.... Analgesic can be given if needed.... Here he has to avoid heavy weight lift or strenous activity... Hot pads can be applied.... Take sleep in posture that not aggravate pain... Healthy and balanced diet given.... For rule out rib fracture chest x ray need to be done.... If needed compression bandage applied.... And yes take care about not bitten by friend next time.....as severe injury can sometime be dangerous... If condition worsen then chest x ray done.... Take care... Dr.Parth