The right dog for my family?

Im looking for a dog that would suit my busy life and children. I should really start by saying that, it would only be on its own whilst I do food shopping, pretty much every where else i go it could come with me. I am interested to know which kind of dog would suit us. My children are 3 and 5 and my eldest is slightly weary of dogs. (He is getting better but when he was young he had a dog jump up his back) I have a horse, 2 cats and a rabbit. I know there is a lot of dogs in animal refuges but up here they are mostly staffs (not against them) but I would rather if I got they type of dog to go to a breeder that knows the history.