Has anyone had a similar experience with this?

[OhMyLord]

Hi there,
First time posting but I really would like some opinions and don't know what to think.
Basic background. OH and I separated last year reasonably amicably. 2 dd's of 6 and 8. They live with me and visit their dad a couple of times a week, sleep over at his once a week. They are happy and settled in this arrangement and teachers at their school are happy and report no problems after the change in their lives.
My problem is this. Last night I went to put them to bed and tuck them in, it was quite late for them as they had watched a film (9pm) As I gave my eldest a cuddle, I noticed a postcard on her bedside table. I didn't recognise it so picked it up and looked at the back.
On the reverse side she had written some really inappropriate sexual stuff about her dad and now I have no idea what to do. As soon as I saw it I said that's really rude ,you shouldn't have done this to her and left it at that after giving her a big hug. I didn't know what to say and now I don't know what to do.
Part of me thinks this could be something she has seen or heard in the playground, or on a computer or could be something more sinister.
I would be so grateful if anyone has any ideas or advice.

Maybe you should try to talk to her upfront about it and see what she says. Kids hear terrible language these days so it could very well be that she wrote whatever she wrote not knowing what it meant.

Thanks for replying. I feel so shaky. The writing was direct and sadly very to the point. I am going to see if she'll talk to me tonight. Any more comments and opinions will be so helpful. I feel like my head is going to explode at the moment.:(

oh dear ohmylord. I think this is a "child protection issue" and needs professional help. I'd be tempted to go to school who will go to the police, but school's involvement may mean the police handle it more sensitivly (this is speculation on my part) and they may be able to offer additional advice and support. School would need to know anyway and have procedures in place for dealing with these things.

Thank you moonface, I have posted this on the relationships board as well as there was only a little response earlier. Now I don't know what to think.

How's it going OP?