If you stay in Shinjuku, it's easy to take the Yamanote Line (silver train with a green stripe) to Ueno, the location of the zoo. It's kind of a sad zoo, however, since the animals are in rather small enclosures. The rest of the park is interesting, though, and your six-year-old may enjoy the hands-on Sh*tamachi Museum on the south edge of the park. It is a museum of prewar life and contains detailed mock-ups of stores and residences from that era, including having ordinary household items and clothing in the drawers and closets.