Cheap and outdoors -- that's how I like my family activities these days. And if we can ride our bikes while we're at it, all the better. So I really love Seattle's Bicycle Saturdays and Sundays (scheduled twice a month through September) -- the four gorgeous, Lake Washington-hugging miles of road between Seward Park and Mount Baker Beach, usually crawling with cars, are closed to traffic. That means that you and the kiddos can ride without choking on exhaust or worrying about speeders. Plus, having the road to yourselves feels luxurious, and there's enough room for beginning riders to weave without crashing into other bikes.
Pack some lunch and find a spot to stop and eat along the way, and plan to spend some time paddling in the water and hanging out at the playground near the entrance of Seward Park. You could easily spend all day here.
I've seen today's hours reported as 1-4 p.m. (in a publication that shall remain nameless), but the city's site maintains that the road is closed from 9 a.m.-6 p.m. today, and I'm going with that. Here's a map for those of you who don't know the area.