Advice every parent needs to hear about firearm safety.

This week, an 8-year-old boy accidentally shot and killed his 2-year-old sister in California.

"It's a tragic case of a sibling who picked up a firearm, thinking it was a toy, pointed it at his sister and discharged one round from the firearm, striking her in the head," said Vacaville Police Sgt. Charlie Spruill.

But these aren't freak accidents. More than 500 children die annually from accidental gunshots. Some shoot themselves, while others kill friends or siblings after discovering a gun.

Here are more scary stats: Americans own 200 million firearms, and 35 percent of homes contain at least one gun. Last year, a study conducted by the Centers for Disease Control and Prevention found that more than 1.7 million children live in homes with loaded and unlocked guns.

And if you do own a gun and think your kid won't get to it, listen to this: A recent study published in the Archives of Pediatric and Adolescent Medicine found that 39 percent of kids knew where their parents' guns were stored, while 22 percent said that they had handled the weapons despite adults' warnings to stay away. What's more, age was not a factor in whether children had played with the guns: Five-year-olds were just as likely to report doing so as 14-year-olds.

Here are just a few heartbreaking cases:

• Four-year-old Dylan Jackson shot himself to death after finding a loaded gun at a friend's home during a birthday party.

• A 3-year-old Southeast Washington boy shot himself in the foot and grazed his hand while playing with his father's gun -- which he found lying on the floor.

• A 2-year-old Tampa boy shot himself in the chest with a loaded 9 mm he found in his parent's couch while playing.

• Last February, a 13-year-old boy shot himself with a semiautomatic handgun in the home of his guardian, a Maryland police officer.

• The 10-year-old son of a New York City police officer died after shooting himself in the face with his father's loaded revolver. The boy found the weapon on a shelf in the basement while looking for a ball his mom had hidden.

Is there a way to stop these senseless deaths?

The NRA (National Rifle Association) sponsors classes to teach children that if they find a gun, to leave the area and inform an adult. But studies show that kids who take these classes are no less likely to play with guns than kids who don't attend the class.

"The biggest mistake parents make is assuming their child doesn't know where the gun in the house is," says Matthew Miller, associate director of the Harvard Injury Control Research Center. "Kids are smart, and if they know there's a firearm in the house, they'll probably figure out a way to get to it.

"We can't expect children to act like adults," he adds. "Parents monitor their kid's diet, curfew and social life, but when it comes to guns, parents often just say, 'Respect the gun; it's off-limits,' or, 'Guns are dangerous.' That type of parenting just doesn't work."

So should parents not tell kids if there's a gun in the home? 

"First, you have to weigh whether or not you really need a weapon," says Miller. "Do the benefits outweigh the risks? If the answer is yes, you must take safety precautions. Be honest with your children. Tell them there is a firearm in the home, but explicitly explain that guns are fatal, no matter how children handle them. Don't keep the gun loaded; store the ammunition in a locked safe and carry the key with you at all times. Also, don't hide the combination and don't give it an obvious numerical password.

"The American Academy of Pediatrics recommends that pediatricians ask parents about guns in their home in an effort called 'Anticipatory Guidance,' which attempts to keep children safe in cars, on bikes and around swimming pools," adds Miller. "It's rare that doctors initiate this conversation, but they should. Also, [you should] ask the parents of your children's friends if they keep guns at home, and if kids will be playing where they're stored. Don't worry about appearing intrusive: It's better to seem pushy and be safe."

Do you think parents should keep guns in their home with children present?