Besides the aquarium -- what other activity would be good for an 8 year old child around the inner harbor?

Just visited Baltimore for one night last weekend- Did the aquarium and dolphin show, and the 7 & 8 year olds were exhausted!There is a big Discovery Zone building there which seems to be aimed towards children, although we didn't get there. Had lunch at ESPN Zone and the game room upstairs is incredible! You could spend hours (and tons of money) up there. Hit Barnes & Noble after lunch at kid's request and they loved that too even though we have one here. Hope someone can give you more info on Ft. McHenry etc. Have fun!

you can also take a ferry to one of the restaurants in the harbor. my kids enjoyed taking a boat to dinner.

Was there around 4-5 years ago. There was a Science Center (maybe that's the Discovery Zone Gail mentions) - it was great for kids and there's an IMAX theater inside, also very interesting for both kids and adults.

The Science Center is different from the Discovery Zone. It is located on the opposite end of the Inner Harbor from the aquarium and has plenty of hands on stuff for kids to try.
In addition, a new attraction has been added to the Discovery Zone-- a hot air balloon that is tethered to a steel cable and can take riders 400 feet up for a great view of the area.
Not far from the harbor is the Babe Ruth Museum. It is located on the site of the house where the Babe was born.
I'm sure you will find plenty to occupy the child in the Inner Harbor area.

Got to go to the aquarium--its awesome. Discovery zones balloon is kinda fun too (although cold weather now?) IMAX at science center is also showing a great movie on the human body (gross stuff like footage of digestion that apparently go over big with the kids)
Torsk WWII submarine next to aquarium
Constellation (sister twin of the USS Constitution--oldest US Naval ship)
World trade center observatory (warmer than the hot air ballon)
ESPN zone if the kid is a sports fan at all
Hard rock cafe in same building
ETC.

Went to the Inner Harbor this past July, (just after the train wreck in the tunnel) as I have done on numerous trips to Maryland & DC. Went to Fort McHenry, which is a short drive from the inner harbor. The kids really liked the fort, walking the grounds going into the buildings & learning about all the historical significance of the place. Then we went over to the inner harbor. We went onbaord the USS Constellation. The kids really enjoyed that also. I enjoyed it also, but not as much as the past 10 times I have been on it. This was the first time I was on it since the re-fit was completed. Before the re-fit it was thought that the keel for this ship was layed in 1797 (& would be a sister ship of the USS Constitution), but during the re-fit, it was discovered that this ship was actually the USS Constellation that was built in the 1850's & used for the Civil War. But still has historical significance. The kids also loved going thru the shops at Inner Harbor & stopping at a seafood place ( I think it was Phillips) & getting their first taste of Maryland blue crab, for this trip. As mentioned before, the Torsk is there & there is also a lighthouse ship in the harbor that can be toured. By the way, the aquarium has a seal pool that can be viewed from the outside, where you can (obviously) watch the seals & sea lions.

Agree Port Discovery, Science Center and Aquarium are great. There is a Visionary Arts Museum within walking distance. Also, the Galleria and Inner Harbor have some fun shops that kids will enjoy. Good kid friendly restaurants too. Ravens football is there as well.