When should I worry about nosebleeds?

My almost 4 year old constantly gets nose bleeds I know it’s normal for them around this age when they pick their nose but he gets nosebleeds at least 4 times a week even when he doesn’t pick his nose, my 11 year old daughter also gets nose bleeds this often and now I’m worried could it be something else? How normal is this? I want to make an appointment with their doctor if it’s serious because they haven’t been out at all since school was closed here in NYC I don’t want to take them out we’ve been in quarantine since March 15