9 year old accessed porn

[maxxymoment]

Please help me work out the best way to handle a situation that happened yesterday.
My dd age 9 was engaged in a face time call on her iPod in our living room with a school friend aged 9 also. I wasn't listening until I heard the friend tell her she was going to "send her some pictures of ladies sucking men's willies". I immediately grabbed the iPod and said to her friend "what did you just say"? To which she replied she was only joking. My 5 and 6 year old children were sat next to my dd and my 6 year old repeated the words back to me so there was no question of what was said. My dh had come into the room at this point. I told my dd to end the call and soon after drove to the other girls house to discuss with her parents. Their dd was upset and they were shocked. I explained the facts, told them how upset I was, said they should check Internet history and left.
They later texted me to say they had checked the Internet history and it would seem their dd had managed only one search and had found a loophole on their Internet restrictions which they've adjusted.
How can I minimise the impact on my dc's especially the younger ones?
I have talked to dd (9) and reiterated how there is lots of things on the web which children shouldn't see but wasn't specific and didn't repeat or relate what had been said to sex. At the time of the incident, I'm not sure she was even listening that closely but my 6 year old definitely heard. I want to gloss over it and not talk about it specifically but don't know if this is correct. My dd has no knowledge of sex at all at the moment. I'm ready, I have books, she knows about periods but the rest hasn't been an issue until now.
For the younger children, we just didn't mention it at all again. My 6 year old is quite bright and I'm not sure they will just forget it and I'm terrified that they might repeat in front of their peer group.
9 year old dd is supposed to be going on a day out with this family at the weekend. In the immediate aftermath of the call, my dh and I discussed her not going but I've reassured her that she can still go because I feel the impact of her not going will draw more attention to the call and what was said. I don't blame the other child of course, children are curious and if the web restrictions are not there... But we have never really encouraged a friendship with this child for lots of other reasons. She likes 1-2-1 friendships, doesn't seem to mix well in a group and tries to manipulate the object of her attention into only playing with her. She once scratched her own face and drew blood when my dd decided to play with other friends at school and blamed my dd. fortunately it was witnessed by others otherwise who knows what might have happened. This girl does appear to struggle with friendships and can be really nasty if she isn't getting her own way. I don't know her parents well enough to discuss that with them but I do know that lots of other parents feel the same and don't encourage friendship for the same reasons. I know that isn't relevant but wanted to give some background info. I try and encourage my dd to have lots of friendships rather than a best friend but this girl has always been tricky and I don't know her parents well or their values.
Any ideas on how to handle this? I'm dreading the weekend where their dd might elaborate a bit more on what she has seen.
Thank you!

[SavoyCabbage]

I would use it as a platform to start talking about sex.

My dd is 10 in November and she doesn't know about sex at all. I'm ready for it too and I'm not embarrassed or dreading it but she's just nowhere near it.

[maxxymoment]

Thank you for the replies so far. I don't think it's unusual for 9 year old to not know about the mechanics of sex. I have had chats with many of her friends parents and they are all the same. I actually only told her about periods because this same girl came into school and started talking about it so I felt my hand was forced on that one. To be fair though, this girl is almost 10 and my dd has only recently turned 9. I don't work in a school though so I'm not used to what they might be talking about. I do work in healthcare though, and I have no qualms about discussing sex or anything else with her. As I've said, I have some books and when the questions flow I will answer them. But she is 9! Do I really use blowjobs as a platform to discuss sex though? My dd hasn't mentioned it and I'm not clear if she even heard what was said clearly. I have thought of telling this other girls parents to censor their conversation at the weekend because I don't want this girl filling in the gaps. I know when they go back to school it would be more difficult. But I feel this girls parents have a lot of explaining and discussing to do with their child. Can I expect them to talk to her about not discussing it with others who may not know. Just as I would ask my dc's to not talk about Father Christmas not being real if they knew the truth and others didn't. (She does still believe btw)
Their explanation re the Internet was that she search via safari and that wasn't covered by the blocks?? He works in IT ffs. They do seem reasonable parents if a little odd. Mum struggles with conversation and eye contact (and has a moustache), in fact they both do. Their dd is an only child. I do exchange pleasantries with her when I see her. There have been lots of little things which I've worried about with their dd. she squeezed her gerbil and it died, accident??? She once told my daughter she would get a gun and shoot her dead. But I do a lot of safeguarding work and therefore might look too much into things.
Thank you again for your thoughts