Hello Mate
I have a German Shepherd, these are great dogs, loyal, obedient, intelligent and great working dogs. I have two small children and the dogs gets on fine with them. The dog is protective of them and when we go for walks will keep an eye on the kids and not let them stray to far.
As stated before, there is a risk getting a dog that has been rehomed, ask pleanty of questions, find out the history of the dog. Go and meet the dog and take the kids to meet the dog also, see how the dog reacts, is it shy, aggressive, does it approach you and the kids with no hesitation and is it friendly.
I got my shepherd from a registered breeder when it was 12 weeks old so paid alot more. This is no guarantee that the dog will be sound but at least this way I met the breeder, met the puppies and met the puppies parents.
I could assess the temperament of the puppy and then look at the dogs parents to see how they were, this gave me an idea of how he would turn out when he was grown.
With kids in the house, their is always a risk, you need to educate the kids not to pull at the dog or poke it etc especially when the dog is new. Once settled the dog and kids will learn each other boundaries and dog should be more at ease. Just be aware with a rehomed dog, depending on the history, this could take much longer.
Hope this helps