HC,
Our family has only had German Shepherds, actually, we are on dog #3 now.
Our first dog was 5 years when we got her and she was absolutely wonderful with our son. We had her first and then we had our son and she never once acted jealous or did anything to hurt him. I still remember him riding on her back when she would sit like she was a small pony! When she got sick, she never nipped at our children either. What worked well was that she had been trained well (before we got her), had a family disposition (a good breeder would know which Shepherds are family vs. work oriented), and because she was older...she was more mellow. The only downside was that she had the long fur and shed a lot--hence the purchase of a good Dyson vacuum!
We then adopted our neighbor's dog--they were moving and couldn't take her. She was 8 when we got her and was also a very loving, gentle dog. She did well with the children and obeyed each family member well. She died of cancer after 1 1/2.
After she died we bought a puppy. While I love her dearly (she has short fur and doesn't shed as much as our other two did), it has been hard work. We've had to do all of the training, housebreaking and she needs to be walked every single day--or they will turn to chewing, digging and other annoying habits to alleviate the boredom. Also, with this type of breed, you have to establish early on that every family member is the "Alpha" otherwise, if you don't, they will try to dominate the non-Alpha's in your family (which are often the children). Hence, it is crucial for every family memeber to participate in the training to avoid problems down the road. If you don't have the time and money to commit to proper training classes, then I would not recommend buying a puppy--there are lots of wonderful older, trained dogs that need homes.
If you have your heart set on a specific breed...be sure to also check "rescue" websites for those specific breeds you're interested in. These people know the dogs they care for extremely well and can place the right dog to fit your family.
Good luck!