Get a little guy like this.
Then have your 6 year old and your new family member go through obedience classes with your 6 yo as the primary handler.
I agree, ours taught our firstborn how to hide bones! When I needed to disipline daughter we had to put Shanna in a bedroom first. She was the best dog, so obedient and so full of humor. Thanks for reminding me of her.
To the original poster about the type of breed she should get...
I believe any dog raised with a child will become that childs best friend and confidant when Mom and Dad are the meanest people on earth. Just make sure the child is shown constantly how to treat the dog and give them responsibilities to help care for the dog. We have had a sheperd, lab, rottie and a bloodhound when my children were growing up. Lab was obnoxious as h*ll but so good with the girls and that is what is important. Sheperd and rottie would have defended each girl to their own death to protect their charges. Both of them would have never harmed anyone unless their girls were threatened. Both also had to suffer through tea parties and dress up time.
I now have Old English sheepdogs and they are just big clowns but do love to herd the grandsons. I do love my OES dearly but they are a little over anxious when it comes to working the kids!
They are known as the nanny dogs and you could lay money down that they would never let the kids stray out of the yard.
In short, every dog has it's valuable traits and if it is raised with a child, what a nice gift and lesson for that child. It teachs them how to love an animal and responsibility for that special family member. Good luck with your search! Fun times are ahead!