Nose picking in children causes sub-clinical infection of nasal mucosa whose elasticity becomes weakened. This results in nasal bleeds with slight trauma like a scratch of a fingernail or tap on nose. First aid in such situations is to have the child sit bending forwards and pinch & hold both nostrils tightly shut for upto 5 minutes with child breathing from mouth. This will stop the bleeding. Icepacks over nose will also help. Blowing of nose should be forbidden for 48 hours as it may dislodge newly formed clot. Now go to nearest good ENT Specialist for further medical management.