Thank you so much everyone for your replies and assistance, sorry I've dug up a few, erm... quarrels for want of a better term.
Well we're off to the vets at 12.30 to seek medical advice, I'm still very much in shock and keep going over everything that's happened, everyone's thoughts and advice and I'm not any clearer I don't think. One thing that keeps coming up in my mind though is that I really don't trust Chloe now, I know we can never trust dogs 100% of the time, I'm not that naive. All three incidents were slightly different and the only running theme is it's been around the same time each day and it's been the kids not me.
It's really difficult for me to try and explain a few things I guess which leave me even more confused. Chloe and the kids rarely have that much to do with each other, the kids' just aren't that interested to be honest! She's my dog and I'm around her, other than overnight when she's in her crate asleep, almost 24/7 so thought I was pretty clued up on her and her behaviour. I don't believe it's a food thing, she wasn't hungry at any of the times anything happened, she was nowhere near her food, her bed, her toys, balls, treats anything.
My daughter told me this morning that before Chloe went for her last night she looked up at Leigh for a moment so clearly saw her and then went for her, so to me that's not Chloe being startled, she looked up and saw my daughter then took action.
Her eyesight - again, I'm pretty sure that if her eyesight had altered in a substantial way to warrant a change in behaviour I would have noticed, I could be wrong and I'll clearly speak to the vet about it.
Behaviour - what can I say? I'm no expert but I know my dog better than anybody else and this is so much out of character for her it really did shock me and I'm pretty unshockable in all aspects of life!
Hormones - this is the only real thing that I can see being the problem and I will clearly be asking the vet for medical advice, the behaviourist last night said that it could be months before her hormones settle but she's not a vet so I won't rely on that until it's been backed up.
I appreciate your advice on training with the kids Mark but I really don't think this would alter the situation, she's not going for the kids due to play or food, other than the first time it happened nobody was doing anything untoward whatsoever.
We've had our usual walk this morning and I've just been going over and over in my head everything, I will wait to see what the vet says but at this moment in time I just don't want Chloe around to be completely honest, my kids mean the world to me and this incident has really shook me up.
I will let you all know how we get on and thank you once again for all the posts on the thread and the pm's which I am on my way over to now to reply to.
Thank you!