Thank you for your query.
Do not panic.
Generally nose bleeds are common in children who prick their nose often.
If he doesn't have this habit and his nose bleeds without any reason then he might need some investigations taking into account his history of nose trauma.
He needs a blood tests,specially platelet counts and probably an ENT examination of the nostrils.
take him for a ENT specialist
if he bleeds any more.Check his blood pressure too.
Hope this answers your query.If you have any other queries kindly direct them to me.Wishing your child a speedy recovery.Have a nice day.