A good breeder will be cautious about selling a dog to a family with no GSD experience and very young children. There are pros and cons to getting a puppy over a rescue dog, the main one being that you can select the dog you want and can socialize and train it yourself to your own standards from an early age. You have a few red flags in your post. The first is "young children." If they are under 6, think twice about getting a puppy, as they need a lot of attention the first year, training, and socialization. There is also the danger that the puppy will think of young children as litter mates and it will take a firm hand to quickly teach them not to nip ankles or jump on your children.
The other is the elderly silky. How well does your older dog do with other dogs and will a puppy be too much for an older, tiny dog?
Both GSROC and Coastal German Shepherds are excellent rescues. If you live in or near the OC, I suggest you contact them first and volunteer to foster a GSD. That will give you experience with the breed, and you usually get first chance to adopt a dog if you like it. You should go into fostering with the idea that you aren't going to keep a dog, and be willing to give it up for adoption if it isn't exactly what you need. I've fostered and adopted my own foster. I can tell you from personal experience that fosters might be on "good behavior" the first month or so, in a honeymoon period, and that if you even sense a problematic behavior, let someone else adopt the dog. Eventually you will find one you love, even if it's not a puppy. Take the dog through obedience, even if it's trained.
Then, in a few years, when your children are older and you are sure you understand the breed, you can bring in a puppy from a breeder. GSDs that are socialized to other dogs, love living on packs, and two dogs aren't that much more work than one.
If you foster, be very picky and clear about what you want. No aggression toward people or animals at all. A dog that is good with children and if possible, already knows basic obedience. The downside is that if the dog has any bad habits, you'll have to work to get rid of them. Both rescues should have trainers they recommend to help you with any problems. Those are the only two GSD rescues I'd recommend in So Cal (I hope I'm not offending anyone but I know people I've met online who have worked with each of them and were extremely happy, no complaints at all).