This jam-packed day of bike fun at East River Park, sponsored by Bike New York, is the one not to miss. Early birds can score the official New York City bike helmet, distributed by Department of Transportation staff free of charge while supplies last. If your child has outgrown her bike, she can swap it for one that fits (also at no cost), thanks to forward-thinking outfit Recycle-A-Bicycle. (If any bikes are left over, they’ll be distributed first-come, first served at the end of the day.) Kids can practice their riding skills—such as cycling in a straight line, signaling turns and scanning the streets for traffic—in Bike Driver’s Ed clinics, or learn how to ride their first two-wheeler in beginner workshops throughout the day. (Class preregistration is recommended but not required; participants should bring their own bikes and helmets.) Finally, the NYPD’s Crime Prevention Unit will be on hand to register kid and adult bicycles, engraving them with registration numbers and unique decals that make it easier for police to identify the owner of recovered bicycles. All ages.