Our ds (12) has just (in the past week) got his first smartphone and joined his school year's WhatsApp, the proviso being we can read the messages any time we want. A few of the kids are using a horrific level of crude and aggressive sexual language that I can't repeat here (basically what they'd do to girls, using derogatory and crude and agressive language). I'm guessing I can't really tell the school (can I?) as it's a 'private' chat. I deleted those messages before my ds saw them but presumably there'll be more. Should I just tell him to come off the group? Tell the school? Tell the parents of the kids? Do nothing?