11yo still picks his nose and eats it

I babysit an 11 year old boy who starts middle school tomorrow and he still sees no problem with picking his nose and eating it. Even his 8 year old brother stopped that a couple years ago.

His parents don't really do anything about it other than telling him to stop, which obviously doesn't help.

Is this normal behavior for a child this age? How can I help get him to stop?