What time of day would this be? Weekday or weekend? Which airline(s)? Security lines at SEA can be terrible, especially on cruise days (Fri-Mon) and with a big party with kids having to queue for an hour to get back airside could be a major pain.

The Pike Place market is enjoyable but can be quite chaotic during cruise season - very crowded and increasingly touristy. It's best in the early mornings which probably won't apply in your case. An alternative, one that can be fun and educational, is a visit to Uwajimaya, Seattle's iconic pan-Asian grocery and department store, located in the International District just south of the downtown core. Uwajimaya is like an instant immersion into the Pacific Rim. Play "name that vegetable" in the produce section, shop for weird Japanese snacks for the travels ahead, have a meal in the cool food court that features stalls from numerous Asian countries. Everybody might get a kick out of visiting a branch of Kinokuniya, Japan's biggest bookstore, located right in the same building. It has more than books - cool gifts and other fun things. I know that touring a supermarket doesn't sound like much of a crowd pleaser, but trust me, Uwajimaya is different.

Uwajimaya - Wikipedia