DD1 has always been a nose picker. Never to the point of bleeding though!
I used to just remind her constantly that noone wants to see it & that if she was desperate to go do it in the loo!
She's 8 now & I can't remember the last time I saw her go for it. A few years ago. I'm not sure if she even still does
I'm glad the other 2 haven't thought of it (yet!)