To tell parents about nasty messages on kids messaging group

[MBDBBB]

My 12 y.o. child is on a message group chat with friends at school. I keep a general eye on it (with my child’s knowledge) and it’s in the main harmless chit chat and posting silly YouTube videos. I have spotted a really offensive message from one member of the group about another child in the year who is not on the chat. My child and another called them out and said they should delete it, but it is still there. I am debating messaging the mother of the child to flag up that she might want to keep a closer eye on what her child is posting but part of me thinks perhaps that would just be busybody behaviour. WIBU to message her?

YABU - mind your own business
YANBU - message her

Wow replies seem a little harsh to my
Friend

From what I gather she only had that girl her so called friend mum dad brother on the phone

Obv didn't expect her best friend from school to say such nasty things

I saw the videos. How a 7/8yr can be so horrible is behind me

Apart from if learnt /repeated off her mum

Where my friends little girl was polite back and told her mum who would have seen the conversation when she checked her phone

Blaming a parent for giving a phone to a yr 3 seems harsh when only those people in her family on it seems harsh

What an uncomfortable situation to be in. The child being bullied online who has no idea and their parents - that’s another level of stomach churning awfulness. My gut feeling is to share this with the school, asking to be kept anonymous. It’s unlikely this is isolated and it’s possible this child is being bullied in other ways perhaps on school grounds / time. Hope that message gets deleted and this behavior stops.

My school would tackle it but they'd make it very clear that WhatsApp isn't an age appropriate platform for this age group!!