Hello I have gone through your complaints.
Nose is a very soft area which is having more blood supply. It is a simple mucosal injury
Even mild injury or stress
will cause bleeding through nose.
Actually there is no need to worry ,if your child doesn't have any other bleeding manifestations.
Just don't expose your child to cold
climate and don't make him to sneeze a lot .
Don't squeeze the nose to extract the secretions.
You can wait and watch.
Thank you. Good day.