Dobermans and kids can be a wonderful combination - my two children now in 1st grade and 3rd grade have lived with Dobermans since the day they came home from the hospital. The key is in training, training, and some more training.... and mucho supervision with young children.
My 2 year old bitch came from a wonderful show/performance breeder and came home with us at 8 weeks. At the time my youngest child was 4 and my oldest was 6. Velma never had a problem recognizing my older child as being "dominant" over her, but did have issues with the younger child. It took quite a bit of work and just time for my 4 year old child to mature a little to get past it. My bitch is a status seeking dog, and a more submissive dog may be easier - not too submissive because then you will deal with fear issues and that is just as bad.
First decide if this is really the right breed for you - they are high energy, intellegent dogs, that are very people oriented. They require a dedication to training, lots of exercise, and lots of attention. If they are the right breed for you, then you will never want anything else after having one.
Second, find a good breeder. Go to the Doberman Pinscher Club of America website www.dpca.org and READ READ READ about what to look for in a breeder. Then start with the breeder list - ask all the questions... don't be intimidated by the fact that they breed top 20 Dobermans - you want a healthy even tempered family dog, and many top breeders produce exactly what you are looking for... but some don't. Be willing to travel a few hours to find the right pup for you. There are several good breeders within a few hours of you. Once you find a breeder - you might have to wait for a litter - it is worth it. Then let the breeder pick the puppy they feel is best suited to your home. This will often be a bitch when you are dealing with a home with young children.
Good luck to you. Dobermans are a wonderful family dog - my family is living proof of that. However, they are not the best family dog for every family. Make sure they are what you want - there are already way too many Dobermans in rescue because of people who wanted one but did not really know what this breed is like.