How on earth do I handle this?

[Foreverwherever]

Ds (4) dd (6) and dneighbours ds (9) playing in next doors garden. I go round and see ndds has shorts down, bare bum lying on his front, ds kissing his bottom! Dd sat playing nearby. I shouted out hey what's going on and they jumped up, hi mum etc etc and I told my 2 to come home.

I had a good chat with ds and apparently he asked ndds to pull down his pants as they were playing babies. I told him it's not right to have pants down etc or to be touching privately. Do you think i need to mention this to ndparents? I've no idea how I should be reacting..

Anyone?

Id definitely mention it to your Neighbour & just keep an eye on them, don't go in all guns blazing though iyswim .
Also have you had the talk with your DC about what is/isn't ok their is a whole thing the NSPCC have done that is really helpful

I think you need to reiterate the NSPCC 'pants' rule with your dc and tell ndns what has happened (in a very non accusatory way!) have you ever had any problems with 9yo ndn before? It may not be a huge thing and my 9yo and 6yo ds' can do silly things like that but its a big age gap and needs to not happen again.

Try not to worry but just keep your eye on them when they play

Isn't there an advert where a mum is kissing a babies bare bottom? Like a sudacrem or Johnson's one?

You say it was your DS who asked him to do it, while they were playing babies, so it's probably just that.

Mention it to ndn just so they can have the pants rule talk with their DS too but it sounds innocent enough