Is this a fashion thing? I ask because a kid from my daughter’s class came around the other day on her bike which had both the front and back brakes disconnected. I explained to her how dangerous this was and spent 15 minutes making the bike safe, it was in a right state the rear wheel bearing had about 10mm of side to side play!
She seemed happy enough and she and my daughter spent the afternoon racing round our street. Later on I saw her and her older brothers bike parked up outside the local shop, the brakes on both bikes had been disconnected again.
Would you have intervened?