Exactly what ofa said.
If you don't believe it you can
A- report the thread. Fine, I'm happy for MNHQ to have a look.
B- click off the page and forget about it.
I'm not concerned with randoms thinking I'm a bullshitter. There are plenty of people with similar experiences, so we're just going to end up arguing about it all bloody day...? Fuck that.
If I wanted a bunfight I'd have asked about ff vs bf!
I'm just here for advice.
I'm not angry with ex at this point - though as I said a bit annoyed he left them with her but I do believe it was a short amount of time and he's capable of using his own judgement and didn't believe this would happen.
As I said I'm not able to speak to him at the moment so just trying to have a think about what would be best; I'll let him talk first but I don't think it's acceptable for her to be around them anymore least of all unattended.
I do think his GF is a knob. But to be fair he wasn't my partner when they got together - we split up when I was just under 8 weeks pregnant - i initiated the split. No cheating and there's no bad blood there or with his gf (prior to now) and they got together not long before I gave birth I have suspected she's a bit of a hanger on but it's not my business and he's bright enough to figure her out eventually. But this has really really shocked me which is why I've just been really angry and not sure how to react as previously stated I don't want to kick off and do something or say something I regret as we get on very well.
He is a wonderful dad, or at least has been up until this incident (I can't speak for whether or not he's being reasonable or wonderful because I don't really know his reaction). He anticipates their needs, doesn't need handholding in the same way that some men described on mn seem to, they're always clean and well fed, always happy to see him, if he has concerns he speaks to me and is always happy to chip in financially as well as making an effort to be around as much as he can (demanding job and big commute). He's a shit husband but I won't fault him when it comes to parenting. I see him as equally capable as I am.
His Gf made a few comments about me and the amount of maintenance he pays and even suggested in front of me that I should be showing that at least x amount goes to food and x amount goes to clothes etc. she even then said oh just give her a voucher for x store and y store (then addressed me by saying oh you'd be happy with that wouldn't you?? Er, no. I can manage the finances of my household without handholding and vouchers!) Im told (by him) they argued about it but that was four months ago and then this happens.... so I think she just fucking hates me for taking money he "should" be spending on her/them. Which is ridiculous as it doesn't even look like they're a defacto partnership at this stage so why is she so interested in his money? 
The more I think about it the more it makes sense hope ex agrees with me. I'd be happy enough with her being away from them whether he wants to leave it or not is down to him but I don't want her around the girls