For those not wanting to leave the Inner Harbor area, there are a pair of Places To Visit right on the Harbor.
The Maryland Science Museum is located at the southwest corner of the harbor. Like almost every science museum these days, it’s got the dinosaur exhibit that shows the geological history of the area, interactive displays illustrating various principles of physics (which kids play with and on without stopping to wonder about the various principles involved), a demonstration theater / lecture hall for showing off visually exciting things in chemistry and physics, and a fairly large exhibit sponsored by one of the area’s major corporations / research centers.