How do I get me and my family to the hotel from Baltimore airport?

Hotel is in downtown D.C. and i think its like a 45 minute drive. I also will havemy wife and four kids (one is infant) and luggage for two weeks. We looked into limos and vans, any suggestions?

Check with the hotel. Some offer free shuttle services. Other than that, if you want to drive while you're in DC you can always rent a car. But public transportation should be easy enough to navigate when you get there, and parking would be problematic. You can also simply look into taxi companies. Some might offer you a flat fare to DC.

look to see if they offer a shuttle van at your hotel, if not rent a car

Hello Mr. Positive,
Call the concierge at the hotel you are staying at. I'm sure they will arrange something for you - that's their job!