It is due to crusts which bleed easily when removed.

Avoid forceful blowing and rubbing of nose

He has to avoid rubbing of his nose. Since the nasal septum is highly vascular anteriorly ( d/t a collection of blood vessels there called Little’s area) repeated rubbing will cause ulcerations over Little’s area causing recurrent bleeds. The child probably rubs repeatedly due to formation of crusts in his nose. Start a saline nasal drops such as Nasoclear nasal drops-2 drops, 3 times a day to avoid formation of excessive crusts and faster healing of the ulcer. Continue the drops for at least 7 days. Again, most importantly the child should avoid rubbing or forcefully blowing his nose.

Get him examined thoroughly. He may be allergic due to which he is rubbing his nose and ultimate causing nose bleed due to forceful rubbing.