Nosebleeds in children are most often due to prominent blood vessels on the front part of the nasal septum (wall that separates the nose into right and left sides) that have burst. This can be spontaneous or triggered by certain activities such as frequent nose digging or violent sneezing. He may alsonbe suffering from Rhinitis (sensitive nose).
If the nosebleeds happen twice a week and he has troublesome sensitive nose, you should consider bringing him to see an ENT Specialist. If the cause of the nosebleed is due to enlarged blood vessels on the front part of the nasal septum, it can be easily sealed off using Silver nitrate sticks.
His sensitive nose can be treated with nasal steroid sprays and antihistamines. For more information on nosebleeds and sensitive nose, do check out my previous articles and answers on Human (below are the links):
Hope this helps and all the best!
