I wouldn't rely on your kids to provide care. Even at that age they get bored with responsibility quickly. (I know I did. Happy enough to train him to roll over etc, less happy to schlep about in the rain picking up poop.)
As a first dog, I would never ever ever go with a puppy. You just need to read the threads on here to see how often that goes tits up.
Also echoing what everyone else says about breeders. "It seems fine" isn't good enough and when you go with a bad breeder, you are supporting animal cruelty. I'm sure you don't want to do that.
I also wouldn't go with a collie as a first time owner, they are hard work (lovely dogs, but hard work).
In your position, I'd probably try fostering a dog from a shelter first. See how you get on, see if it fits in with your lifestyle, see if your kids actually take responsibility. You'd be doing the dog a favour too, getting them socialised for a new owner.
Even having grown up with dogs my whole life and having fostered dogs, I was pissed off and resentful of my dog for the first year or so. He was harder work than my babies, and I'm not exaggerating. Prepare for that to happen to you too, it's very common to get "puppy blues" or "rescue regret". Look it up. It's usually temporary, but it happens.
Investigate things like boarding, pet sitting, groomers etc BEFORE you get the dog. Make sure there are decent facilities in your area - it is near impossible for us to find suitable boarding for our dog which makes going on holiday very difficult and stressful. Remember that the dog can't be left alone for more than a few hours, so family days out shopping or doing anything not dog friendly will be much more difficult - I don't remember the last time we spontaneously went on a day trip to another town without the dog, everything has to be arranged in advance.
It's easy to go into dog ownership blind and think it will all be lovely walks and nice cuddles on the sofa. But it can also be stressful and restrictive. I love my dog, he is my best friend and I adore him, but it is hard too.