Your kid wants to bike fast and far, with the wind in his face and the dog loping behind. But sometimes the helmet sitting atop his noggin isn’t doing its designated job. It might be damaged or dangling loosely—or even forgotten all together. Donning a bike helmet can reduce the risk of a serious brain injury, yet less than half of kids under 14 wear one. In fact, more children ages 5 to 14 are treated in the emergency department for bike injuries than any other sport, according to Safe Kids Worldwide.

Fitting your kid for a helmet can be tricky—and nagging him to wear it is rather tedious… Check out our guide to the top four mistakes parents make and your young rider will cruise safely this season.

Mistake #1: Using a damaged helmet

A few nicks in the paint or design won’t affect the way a helmet protects the head, but if the damage is more significant it shouldn’t be worn again. “The polymer foam lining inside a helmet is meant to crush on impact and absorb the energy of a crash, sparing your head,” explains Shane MacRhodes, of Safe Routes to School, a national program that encourages kids to walk or bike to school. Once the foam has been compacted (you might notice cracks in it), the helmet can no longer work effectively. As a general rule of thumb, don’t use a helmet that’s more than 5 years old, says MacRhodes.

Mistake #2: Not checking the fit yourself

Don’t let your kid dash out the door to ride without taking the time to do a quick helmet inspection, recommends Gary Smith, M.D., director for the Center for Injury Research and Policy at Nationwide Children’s Hospital in Columbus, OH. The helmet should sit level on the head, resting two-finger widths above the eyebrows and fit snugly, without moving more than an inch in any direction. Check that the side straps come to a point just below the ears and then adjust the small tabs on the straps until they are about ½ inch from the ear lobe. The chinstrap should be about a ½ inch from the chin when his mouth is closed.

Mistake #3: Forgetting to wear your own helmet

The same house rule regarding seat belts in the car should be applied to bike helmets: everyone wears one, period. “It’s hard to get your kid to put on a helmet if you don’t do the same, so model good behavior,” reminds MacRhodes. Let your kid see you take the time to adjust your own straps and he’ll pick up the importance of getting a good fit each time. You might also shop for the helmet together and let him personalize it with stickers (he may be more apt to wear it if he likes the look!)

Mistake #4: Buying a used helmet or passing one down to a sibling

If the helmet has literally been sitting on the shelf, unused, then it’s fine to consider it for a younger child. “But if it’s seen years of sweat and wear and tear, it’s probably not in the best condition and should be retired,” says Joseph O’Neil, M.D., a member of the American Academy of Pediatrics’ council on injury, violence and poison prevention. Picking up a used one at a yard sale may seem like a cost-saving measure, but it’s also not a good idea. “Not all crash-related damage is visible, so your kid may not be fully protected,” he explains.

Jennifer Kelly Geddes is a New York City-based writer and editor who specializes in parenting, health and child development. She’s also the mom of two teen girls.