Hi,
Yes they should have been wormed by now - and 6 weeks is to early to be leaving mum.
If a rescue is not an option for you (it wasn't for us as we couldn't rehome with kids aged 3 and 5) - then try and find a reputable breeder, then all parents will be health tested, producing clear pups.
But as people on here have said, the rescues are full of Staffies, and they make fantastic pets! (I can see myself with a rescue in a few years - although hubby may not agree
)
Good luck and let us know what happens!