Rainycity, I don't know any such rivers for steelhead fishing, but I've thought a number of times that a perfect river to take the kids to, either to teach them to fish or to fish without many people around is the Tucannon. It's a small, manageable stream, has tons of fish, they bite enough to really keep a kid's interest up, in places there is plenty of room to fish without snagging and hanging up in trees, and there are never many people around. It is my favorite trout stream in Washington and a perfect one for the kids. It is a push to get there from Seattle (I'm from Tacoma), but worth it once you arrive! Good luck.