Have you heard of Fishing Kids? Thanks to a non-profit called Cast for Kids you can take a 5-14yr old to a lake and get a t-shirt, kids rod & reel, and a small netted area teeming with trout (some very big). There are two events on May 2nd at Greenlake (free!) and June 6th at Renton ($10). You need to register online for both events with the Seattle & Renton parks department. It’s great fun and the kids are guaranteed to catch two fish. If you stick around at the end of the day they release the remaining fish into the lake.
They also need volunteers to bait & remove hooks, and clean fish. Sorry, no fly fishing or catch & release until after the event.