Apple

Does everyone really have one? They will soon enough. While currently 30 percent of kids 4 to 14 have a digital-music device, that number has jumped from only 6 percent in 2005. In the next few years, it will be a majority. For kids 13 to 17, 92 percent own some type of music player, and for 86 percent of them, it’s an iPod.

What age to start: The main concern for small ears is hearing loss over time. “The sound an earpiece generates in a smaller ear, as opposed to an adult ear, is more intense,” says Brian Fligor, director of diagnostic audiology at Children’s Hospital in Boston. At age 7 or 8, kids are probably mature enough to stick to volume limits you set.

As they grow up: Set rules on how long they can listen, not just for safety: They’re also not engaging in family life. Kids can listen at 70 percent volume for 90 minutes a day without increasing the risk of hearing loss; at 100 percent, only five minutes are safe. Check Apple support to learn how to lock a maximum volume on an iPod.

Causes for concern: Don’t choose over-the-ear headphones thinking they’re safer than ear buds. Earplug-style headphones (the ones that go into the ear canal) may actually protect young ears, because kids tend to play music at a lower volume with them. Use iTunes parental controls to keep tabs on downloads.

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