My kids have wanted a dog for a very long time. When we moved I told them if we find a house that has a decent yard and a place to put a dog run outside then we could look at getting one.
First task they have is to pick a type of dog they want. There are so many different dogs and they have a huge job ahead of them, so better to start now. The dog will have to be good with kids, low or no shedding, smart, and not too big (afterall we live in a city not the country).
Second task will be learning as much as they can about the breed so they are prepared to take care of the dog properly.
Helpful sites on Pets:
Pet Care Education - easy to navigate and packed full of information.
I'll add sites as I find them. If you know one I should check out leave it in comments.
Click to view please image on merchandise