You're hitting the gas so you can zoom, zoom, zoom up the hill and then -- woooo HOOOO -- you're catching air! All four wheels are off the ground and you land with a thud, sending up a spray of sand as you head off toward a tight curve.

That may sound like a video-game moment, but it's something kids really do when they ride all-terrain vehicles. About the size of riding lawn mowers, ATVs are four-wheeled vehicles equipped with engines that can go as fast as a motorcycle.

As fun as they are, however, ATVs also can be dangerous.

The number of children under 16 who have been hurt or killed on ATVs has risen as the vehicles have gotten more popular in the United States. (See charts.)

In April, 9-year-old Brad R. McDonald of Anne Arundel County died in an ATV accident. Brad was wearing a helmet, goggles and protective clothing when he lost control of an adult-size ATV.

"I wouldn't recommend any kid hopping on one. They could ride it 100 times and be fine, and then that one time, not be," Carlton Powell Sr. said recently. Powell's 14-year-old son, Carlton (known to the family as "Junior"), died in 2003 when he lost control of the adult-size ATV he was riding at a Laurel gravel pit.

Although Powell wants to spread the word about the dangers of ATVs, he knows their popularity makes it hard to protect kids from them.

"They're going to keep selling them," he said. Maybe the best thing "is to make sure there are safe, supervised places for people to ride them. . . . But these accidents keep happening."

Few Rules for Kids

In the late 1980s, the federal government banned three-wheeled ATVs, saying they were too dangerous. However, the industry still makes the four-wheeled kind. The rules for riding them vary from state to state.

There's no ATV age limit in Maryland, except for some designated spots on state-owned land where riders must be at least 12 and have an adult with them. In Virginia, the age limit is 16 for adult-size ATVs and 12 for the youth models.

Recently, doctors and other groups asked the federal government to do more to keep kids from being hurt on ATVs. They want to get children off the adult-size ATVs, which can weigh more than 500 pounds. Children don't have the body weight, strength or judgment to control them at high speeds, medical experts agree.

ATV critics have asked the government to make it illegal for dealers to sell new adult-size ATVs if they know the vehicles are going to be used by kids. Dealers point out that most adult ATVs are clearly marked "not for use by children under 16."

Parents' Responsibility?

Not everyone agrees that more rules are needed. ATV makers say their products are safe if used properly and that the proposed federal law would be too hard to enforce. They say it should be up to parents, not the government, to make sure that kids who ride ATVs get training, are supervised when they ride, wear the proper gear and ride a vehicle that's the right size for them.

Crystal Landry, 15, of Accokeek, has ridden ATVs since she was 3. She rides an adult-size Yamaha Blaster and says she follows her parents' rules. "I can't ride without people with me," she said. ". . . I stay far back from other riders."

Crystal, who once broke her wrist on a jump, said she believes safety is important, but that she mostly rides ATVs for fun. "I like to go fast and see if I can jump. It's a very fun sport if you know what you're doing."

-- Fern Shen

Carlton Powell Jr., 14, was killed in an ATV accident in 2003.The largest ATVs can weigh more than 500 pounds and are not safe for kids.