There has been some nice staff bully breed xx etc on one of the organisations but they all seem so big - although they are classified as medium sized dogs. Seems to be quite a few Amstaff (?) crosses but very few or no staffords. The kids are used to a certain size of dog and I don't want to overwhelm them with a big dog.
As regards gumtree. There is an element of risk there, for sure. But there must also be dogs there that need some love, regardless of their origin. Bringing Serena along is a must, as you said. I guess its just a matter of being careful.