From SFBC:

Join the SF Bicycle Coalition, parents and kids as we enjoy a car-free day in the park with fun bike-related family activities, like out Freedom from Training Wheels program and a Bike Road-eo course that teaches two-wheelers (with and without training wheels) basic bike skills. Show off your baby bike seats, trail-a-bikes, and Xtracycles (or however your family gears up), and get advice at our Family Biking Showcase. Participate in games, a bike parade, a scavenger hunt and more! Free! For more information, visit http://sfbike.org/familyday.