Sexual talk in school

[Stepmum95]

My partner got a call from my 10 year old stepsons (I'll call him J) school today to say he'd been arguing with a girl (I'll call her K). K and J have had issues before as it was reported that J has sexual stuff to K in the past - we don't know if that's true or not but it's been dealt with and he was told to stay away from her so there were no more problems. For context, J told us that it was K that said it to him rather than vice versa.

Anyway, today the school called to say they had been arguing and when we asked J what happened, he said that his best friend (I'll call him R) told K that she wanted to 'suck J's ___'.

I'm (I think rightly) concerned for several reasons:

1. It's another problem with K, and of a sexual nature.
2. This is K's best friend, who he's spent a lot of time with - what else has he said that teachers don't know about?
3. Where has R learnt this language? What else does he know? (To be clear, I know it is his parents that need to deal with this but J goes to his house in the mornings to meet him for school - are the parents there? Do they think it's okay?)
4. J is easily influenced, and like most children just wants to be 'cool' - is he going to start repeating this to others etc?

He's only 10, in Year 6, and I think it's very early for him to know about sex in this capacity (sex education in schools will cover puberty and 'baby making') but do we tell J that he needs to stay away from R? Or do we let them be friends and tell him to not repeat any of the language his friend has used? Or do we go with the fact that it's been said and have an early birds and bees talk (he feels far to young for this)? Or a combination of the above? Or am I worrying unnecessarily and it's normal for kids at this age?

I'm not a birth parent but my step-son lost his mum about 8 years ago and clings to me as a maternal figure, and calls me mum/mummy. It's a bit of a minefield and I've jumped straight in at the deep end with a 10 year old who is rapidly approaching puberty!

Any thoughts/help/advice are gratefully received!

Had similar with my daughter at the start of year 7. School treated it as sexual harassment, separated them and got DD to provide an impact statement which the boy had to respond. I had spoken to his mother first to try and keep school out of it but she demanded that school deal with it. As she found it so easy to outsource parenting I mentioned to the teacher involved that I was concerned it was a safeguarding issue as the boy was clearly watching/had access to adult content somewhere.