Took my brother's kids to the top of the Tokyo Tower last week. They loved it. You can't go to the tip top (the thing is 333 meters high) but the top "special" observatory is a respectable 250 meters up, and there's a cool glass elevator.
Click here, here, and/or here to watch some video footage that I posted on youtube. (Warning: these videos are probably boring if you don't know me or my brother's family. The first clip features a 6-year-old's monologue, accompanied by shaky camera work; the second gives a glimpse from the "lookdown window," and the third is what you see and hear from inside the elevator.)
The Noppon brothers -- twins born in 1998 -- are the Tokyo Tower mascots. The one in red overalls is, according to the official website, "cheerful and lively, but often feels lonely and misses people." His twin wears blue overalls and is "shy and cool."