@Busy Mom there are a bunch of things to do near Baltimore.
The Star Spangled Banner was written right in the harbor out from Ft. McHenry, it is a beautiful fort with TONS of history and you can go all through the fort.
There is the Babe Ruth Museum, right down from Camden Yards baseball park, M&T Bank Stadium where the Ravens play. (both stadiums offer tours of the parks).
Fells point and Little Italy are great places to visit.
There is a ton of civil war trails around. There is also a free bus that will take you all around Baltimore.
Then you can also go to Port Discovery, it is a huge indoor play/learning area for kids (and grownups) They have a 4 story jungle gym inside with rope bridges and slides, the adults play on this also.
As was also mentioned there is a metro system to DC, a world of things in DC.