Hi daffi, some good advice so far, I just wanted to wish you luck in your search.
I have a Border Collie, and he is entirely unsuitable as a dog for children-we have to steer well clear of kids in the park. However, he came to us late with no socialisation etc. and I know of some families who have BCs who are very child-friendly. They aren't traditional pets, though, as has been said, and you will need to work very hard to ensure a balance-a bored or lonely Collie will be a little neurotic (or a lot neurotic!) I only have first-hand experience of my own, so can't speak for all dogs or owners, but there is no chance of a "day off" with a Collie-whereas some breeds can go without a long walk for a day, Jack is bouncing off the walls by mid-afternoon if I haven't had him out to the park with his frisbee! I know you say you're happy to give lots of exercis, and that's fab, but I know also that family life can sometimes overtake, and there may be a day when there's just too much to do to fit in a long walk or two as well!
Staffs, if trained well, are meant to be great with kids, but can be snappy with other dogs, I am told. Even if you don't pick a rescue dog, your local rescue centre will have lots of advice to give you. I am usually keen to suggest a rescue dog, but it can be hard work, and isn't worth risking your kids' safety for.
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