The puppy is only six weeks old and you just brought her home. It will take time for her to settle in and she hasnt even reached the critical socialization point yet. She's recently undergone a very traumatizing event (removal from mom) and it can take puppies a while to settle in. While I think six weeks old is too young for a puppy to be removed from mom (I prefer 8 weeks at least), I would recommend getting in touch with a trainer sooner rather than later. I really recommend positive reinforcement as the primary training method, especially since this will be a child's dog.
GPs are not without their challenges, but with proper socialization, they have the potential to be great dogs for children. It would be a good idea to research the breed so you know what to expect (ie. they are not good candidates for off leash life).
I know you want a dog for protection, but it is always a good idea to socialize and desensitize dogs, otherwise the potential for a reactive, aggressive dog is quite real. This becomes a problem when visitors come over and suddenly you have a very large, reactive or aggressive dog that is difficult to manage. I would outline the behaviors you want to train the dog for and then create a plan to help you teach and reinforce those behaviors. Again this is easier with the help of a trainer, especially in the beginning.
X2 on all counts