Sorry, but I'm another don't get a dog (yet).
I work in a vet hospital, love animals and have always had them, and yet we found ourselves without a dog from the time my first born was 1.5 until he was six, second wasn't born and then almost four. Previous dog was and old wonderful 15 year old lab when we had to say goodbye, and we still watched her like a hawk with the first.
About a year ago we got a shelter dog (for ME specifically, no one else, but the kids and hubby love her and the feeling is completely mutual). We started training with her the week after we brought her home, and we still work with that trainer (not twice weekly, as initially, but still a couple of weekends a month). The costs of training were completely unmustachian but a necessity in my mind, in spite of knowing what to do I needed to be held accountable to someone else, and my hubby grew up with outdoor dogs. Someone gets up at 5:20 every morning to run her, we take her out to chase a ball as soon as we get home. We have to arrange dog care if we're going to be gone overnight and I usually have someone check in if hubby is traveling and I have a long day at work.
I think dogs are an important part of a kid's life, and studies have shown that kids who grow up with pets have less allergic disease. But they will do just fine without them until you all are on the same page about whether you should have one, and are starting to see the light at the end of the tunnel that is a new baby. It's hard enough, don't make it harder. And then, when you're ready, evaluate your kid, the time you can spend with the dog and decide on a breed, or better yet, pick out a three year old whose personality is debeloped and more testable.