Size it up: Kids' bikes come in three sizes: 14-, 16-, and 24-inch. He or she should be able to stand comfortably over the top tube. Upgrade often—better to buy a yard-sale bike that fits than a pricey one that doesn't.

Play games: Training wheels are fine for building certain skills—pedaling, braking, even crashing—but not for balancing or turning, which will require leaning when the wheels are off. Hold a braking contest using a chalk-line target, and use cans for an obstacle course.

Cover up: This is not an option. Get a basic round helmet, certified by CPSC, ASTM, or Snell. Make sure it covers the forehead and the straps are tight enough to fit just one finger between the strap and chin.

Look it over: Kids' bikes are cheaply built and break easily. Start your search at a bike shop, not a big-box store. Look for: bearings instead of bushings on the wheels; spokes instead of one-piece wheels; plastic (not sharp metal) fenders; and at least one rear hand brake (for those panicky moments when her feet slip off the pedals).

Crash smart: Tell him or her that everybody crashes. The right way is to step over the top tube, tuck a shoulder, and roll without sticking an arm out.

Set it up: Adjust the seat so that when the pedal is at its lowest point, the knee is almost straight. Put the handlebars high enough so that her elbows are slightly more open than 90 degrees.