The other day I sat my family in front of the TV to watch Up, the fantastic film by Disney/Pixar, which is called "Uncle Carl's Flying House" in Japan. I'd seen the movie in the States during the summer, so I knew they'd love it, and I wasn't disappointed. When world-famous explorer Charles F. Muntz shows up in his cool-looking airship, my wife said, "Oh, I know what that is, it's a blimp." This is a bit of a running joke in my family because "blimp" was the first English word that my son knew but my (Japanese) wife did not. We've always helped our children grow up to be bilingual so they can enjoy the benefits of both Japan and the U.S. freely, but of course there comes a day when your kids surpass your own linguistic ability. That day came when my son was five or so and called out to a blimp that was flying overhead, causing my wife (who had never encountered that word) to get flustered at how he'd managed to learn a word that she didn't know. When my kids were younger, I'd have "kanji battles" with them to see who could write more characters, and they tried very hard to beat the gaijin only to be vanquished. Now that they're older and my constant use of computers and the Internet has eroded my kanji-writing ability (a phenomenon which plagues native Japanese, too), they can both kick my butt quite easily.
We try to help our kids grow up bilingual, as much as we can.