Bothell/Mill Creek area:
In Tambark Creek Park there are Lego Trails (Legos) and Cretaceous Cache (dinosaurs) and two others. In the Park & Ride where Bothell-Everett Highway crosses 405 (no walking!!) there's Used Cars (Matchbox cars), and Gotta Cache 'Em All (Pokemon theme, also very little walking) is nearby. In Thrasher's Corner Regional Park (undeveloped) there are two caches: Akela's Cache and (my) Keep on Looking!, both of which had kid-type swag in them last time I was there. There's also Walt's Vault Reopened (Disney theme, also very little walking) not too far away. If you were to venture a little farther along Bothell-Everett Highway to North Creek Park, where there are several caches, you'd find Sam's North Creek Croakin' Cache, a fun puzzle with a cute container that would appeal to a little boy (no swag, though!), and 13 Steps to See Dee Cache, a mini-multi with a cute resident TB is nearby.