Hello dear, The bump formation and soreness is due to the impact as well as accumulation of fluid & blood. The blood cells accumulated are eventually broken down and absorbed in the body. But this is a slow process & takes times to disappear completely. Till that time, symptomatic relief is obtained by analgesics preparations (like paracetamol), ice compression & adequate rest. If it still persists or there are any other associated symptoms like fever, vomiting, loss of consciousness, convulsions, etc...then it will be better to consult his Doctor. Under such circumstances, a proper clinical+ radiological evaluation will be needed to rule out any pathological cause for symptoms. Till then, maintain adequate hydration & nutrition status. There is no need to worry, your son will be fine. Wishing him a good health. Take care.