I saw a wonderful idea of cat-proofing your garden at the tica show at the weekend - ooh, just seen that it is the link that Leah posted above - Katzecure – cat fencing for cat breeders and cat owners alike

I understand that it is very tricky when you have young children, but you need to be so careful, cats are very sneaky.

I only ever open my windows a tiny crack, and i then weigh down the latch as one of my cats is ridiculously intelligent and can work out how to lift the latch if i don't!

Take care - i hope you manage to come to a solution, but in the mean time - maybe just don't let your children open the outside doors without your say-so?