don't oil anywhere near the pads or brake disc.sounds like the brake pads have worn down,the grinding noise isn't a good sign.try to refrain from riding until brake pads are replaced as damaging /scoring to the brake disc is eminent.if your son has been riding the bike for a while with this problem you will have to replace the brake disc as it will be scored.brake pads cost around £8.00 disc £25 plus.
ozone, December 2011
