HELLO AND WELCOME TO HCM FORUM,
As you described,the bleeding started once your son woke up from sleep.
This may be due to many facotrs-
tongue thrusting habit
associated tooth infection
which has spread into periapical area
I would suggest you to visit a physician as well as dentist
for direct clinical examination.
Please do not take antibiotics without medical supervision.
Treatment can be planned based on the diagnosis.