Staffies are meant to be excellent family dogs, very good with children. However, as with any dog, its character will be largely formed by how it is treated. This is something you have to consider if you get anything other than a puppy, unless you have a full history and confirmation that the dog is OK with children.
Having a dog can be a wonderful thing (we have a rescue dog, but my children are older) but there is a lot of work involved. Has your dh indicated that he will be fully responsible for exercising the dog, clearing up its mess, etc.? If not, then that onus will fall on you and, if you are not 100% happy with that, then the dog is likely to suffer. I would recommend buying dry food, as it makes their "doings" easier to clear up and is, in the long run, cheaper. I buy a brand called Supadog from my local pet shop (not supermarket) and this costs me about £14 every couple of months. He does have additional treats now and again, and is a very useful waste disposal when the children don't eat their food (much better than me eating it!).
You do have to take into account vaccinations and I would advise taking out some form of pet insurance to cover large vets' bills and also in case the dog causes an accident (although you may already be covered for this through your household insurance). I use Tesco pet insurance which costs just under £10 pm.
On the plus side, I exercise more because I have to walk the dog, the children absolutely love him and it's wonderful to come home to an empty (of humans) house and be greeted by someone that loves the bones off you!