What to Do: Odaiba and Maritime Museum
Fairly new, Odaiba is a combo residential, shopping and play area built on reclaimed land. You can reach it fairly painlessly by taking the Ginza Subway line to Shimbashi Station, then transferring to the Yurikamome Line. The latter line is a monorail-tram thing that winds a big loop around water-front Tokyo before crossing the Rainbow Bridge. It is only about 10 minutes' ride from Shimbashi though a bit dear at Y370 per adult. Nice views at night, including a huge ferris wheel further outside of Tokyo.
Once across, there are a few things to try out.
If someone in your family likes ships, modeling and/or history, you'll need to check out the Museum of Maritime Science (get off at Fune-no-Kagakukan Station on the Yurikamome Line; upon exiting you'll see the Museum in front of you. It is shaped like a giant cruise ship, so you can't miss it blindfolded in the dark).
Outside (for free) you can see two deep sea research submarines, a giant catamaran as used by Japan's navy and Coast Guard, and a huge four engine WWII flying boat (an “Emily” for those who care). On the other side of the museum (still free) is a 14 foot 1/20 scale model of the WWII battleship Yamato. Tied up along side of the museum are two real ships; one is an old ferry and the other is an Antarctic research vessel. You can inspect both ships from the dock for free, or board them for about Y600 per adult and Y350 for kids.
The Museum itself costs Y700 per adult and Y400 for kids, though you can buy special discounted tickets that let you board the ships outside and see the Museum. Once inside, you can look at 1/50 scale models of dozens of commercial ships, including tankers and container ships. There is a separate room devoted to ship propulsion, centered around a real ship's engine, some three stories tall. There are buttons to press and videos to watch all over, though signage describing the displays is pretty much 100% in Japanese.
Parents: there are clean toilets throughout the building, and elevators for handicap and stroller access. Watch out on the fourth floor for a cheesy radio controlled boat pool that costs Y100 a turn. Instead, steer the kids to the 6th floor where they can “drive” a boat in a computer simulation for free. The Museum has only a psuedo-Chinese restaurant, which did not look so appealing, and some ice cream vending machines. There are tables outside if you bring a lunch on a nice day, or, you can find McDonald's and other fast food outside of the Museum, at a nearby mall.
The Museum's web site probably isn't much use unless you read Japanese or just want to look at the pictures. It does, however, features an animated sea capitan with a parachute and a jet-powered butt. Quite charming in that odd Japanese way. You kind of have to see it.
Like I just said, outside of the Museum there is a huge shopping mall a short walk away. For those coming right from North America, you can probably skip this, as it will just remind you of the megamalls back home. For those living in Asia, the mall is probably worth seeing just ‘cause it is unusual for these parts. There is a full-size Toys-'R-Us on the lower level, and a food court with decent Indian, Hawaiian and regular fast food foods.
The shops run towards the trendy and expensive, but there is plenty of room to browse and cruise around on a rainy day. Inside you can also find a “Wild Things Cafe”, a theme restaurant based on the kid's book “Where the Wild Things Are”. Prices run about US$10 per person for hamburgers and the like, but do also get your kids access to an enclosed play area, so the cost may be worth it if your kids need to run off energy and you don't.