Honestly, I personally think you guys should wait. GSDs go through a landshark phase, and they are a LOT of work in general. Of course all puppies are, but GSDs especially. A puppy and a 4 month old baby really just isn't a good idea. It's a lot of work to have one or the other, both requires a very skilled person. It also requires a lot of money. Kids/babies are EXPENSIVE. And so are puppies (what with shots, the cost of buying the actual pup, food, dewormings, any sickness, etc).
I believe we have another member who loves pit bulls, and she could probably tell you more about SBTs than me (they are far more similar to pits than GSDs).
If you decide to get a GSD, TAKE YOUR TIME. Do your research on the lines, their temperaments, pros/cons, training, proper diets, etc. Find a reputable breeder (members here can point you in the right direction). Put down a deposit, and wait for the breeder to have a puppy that will fit in with your family.
Also- Make sure it's what you BOTH want. Any negative feelings towards the pup for not being your chosen breed can have an effect.
Mom To~ Dakoda (b/t GSD), Acheron (black GSD)