Oh yep, this is very much my lane right now (sorting a breed database to give info to new owners)...
1 - under NO circumstances do you get a dog to act as protection for family. Do not do it, it is fucking dangerous. And certainly not if the plan is to send the dog off to be trained using shock collars and prong collars or if DH is a newbie to bite sports and fancies a crack at them. Just don't.
2 - those breeds, no no and no.
Gsd - damn near impossible to get a healthy one outside of working lines and you absolutely do NOT need or want a working line gsd at this point. So many have dodgy temperaments, do you want to be rehabbing a reactive fearful dog for the next four years?
XL Bully - unhealthy, poor temperament, 99% of breeders I wouldn't buy a soft toy from. Too big, too dribbly, don't do it.
Rottie - again, as puppies these are clumsy and daft, they are FAR too easy to misunderstand, mishandle and fuck up, and the only breeders willing to sell to someone who wants a protection dog, and has a 6 year old in the house is again, someone i wouldn't buy a soft toy from.
Examine EXACTLY what H thinks he wants from a 'protection' dog.
MY goal from a dog that will keep me safe is - big enough that people think twice, superduper incredibly easily trainable such that I can teach a big bark and a growl on cue, but of the temperament that ACTUALLY thinks everyone in the world is a friend.
This way I can cue the scary 'fuck off right now or ill eat your face' behaviours, but should an accident occur, no ones actually getting injured.
The probably with many of the 'protection' breeds is that they're either TERRIFIED and highly likely to make mistakes (GSD, Doberman, this is why police are now using Malinois) OR... they are high as kites off their tits wanting to BITE stuff, and if not intensively trained and super well managed will bite the wrong people (see, police dogs biting the wrong people, quite a lot).
So you want a dog that looks the part, can be trained to bluff, but is in fact safe as a dog can actually be.
If Husband actually wants to do some dog sports and training and isn't just thinking of his ego... then:
Picardy Sheepdog is a good choice, some of the same traits of the GSD, a courageous nature, very easily trained, sufficiently large most people think twice but not so large they're a pain in the arse to house, and being a rough coated shaggy breed they also take people by surprise... and don't shed like a GSD.
Superduper well bred Mastiff - not so easy to train, far better temperament and health than the XL Bully. They do shed needle like hair everywhere that is a pain in the arse to get up and they have a tendancy to smell a bit... cheesey.
Large Munsterlander - from the gundog group, not quite a setter, not a spaniel, bigger and more robust than the latter but less scatty than the former, very trainable, willing to do fun training and dog sports, easily trained to growl and bark on cue.
Briard - similarly capable as the Picardy, their roots are in droving and guarding livestock on the move, very trainable, very loyal to family, something that you would shit your pants if it growled or barked at you on cue. Downside is of course theres a LOT of grooming of one of these (but they don't shed much at all!).
If you discount the protection aspect (and i REALLY would) though I'd recommend a Standard Poodle if someone really wants to do some training, and a Deerhound if you want a big dog that is easy going, doesn't shed much, wouldn't thankyou at ALL for attempting dog sports and is generally very economical on space around the house (yes, I have had one in a very small house!).
I would wait until child is a year or two older for the latter two, and more like three years older for the rest, but you know your child and your ability to ensure child follows instructions and doesn't mither or become magnetized to the dog!