sorry this is so long- I can't sleep and have had way too much fun looking at bikes online...
I just wanted to say that I LOVE that you're going to commute and bring the wee one with you!! Most people wouldn't even consider it ("There's no way I can commute, I have a one year old to take to daycare"). Where others see obstacles, you see an opportunity!
What about a cargo bike? If you want to seriously commute and want a bike that will grow with you over the years and serve as true transportation until your little one is old enough to bike on their own- a cargo bike might serve you well. And it will serve you well after your wee one has grown up as a great urban utility bike.
What about a Madsen bike? They are a Portland based company. In the back bucket, there are seats for the kids and built-in seat belts. Kinda cool! I really like the bucket in the back. It's rated for up to 600 lbs. Put the seat in and belt the kiddo, or remove the seat and do some serious hauling. The blog on their site has some great stories of how the bike is used. I'm enamoured by these bikes.
ThisTrek is built for serious hauling. You could put a child seat on the back, and as you little one gets older, they can still ride with you just by sitting on the rear rack (sans child seat).
Or a Surly Big Dummy? Or a Yuba Mundo?
Truth be told, I've always had a thing for cargo bikes, tho. They are beefy and beautiful and meant for serious use. And bonus, you can stop by the store on the way home from the office with the kiddo and load up with groceries.
If you didn't want to go the cargo bike route, what about the Trek Belleville? They used to make a women's mixte version, but it's no longer available. This would be a good sturdy alternative.
And while the price might seem high at first, if you were to just get a standard flat bar bike, by the time you add in fenders, lights, child seat, rear rack, front rack and panniers- the cost is probably the same. Many of the cargo bikes come with fenders and racks (and some with generator lights). You could add it up both ways, but I'm guessing the costs would be similar.