Why they do it:

Like toddlers, the 3-to-5 set has a low threshold for frustration. Plus, they're going through a lot of changes — such as starting school, facing a new baby sib, or graduating to a big-kid bed—that make them extra hungry for your attention, even if it's the negative kind.

How to stop it:

The great thing about preschoolers is that they can still be distracted by a clever trick. For instance, Debbie Granick of St. Louis uses a "whine" cup, or bowl or bucket or whatever's at hand. "Whenever one of them starts, I say, 'Here, go pour out your whine and bring me your regular voice.' It gets a smile, or at least that 'Oh, Mom' look, and then they'll usually change their tone." She then thanks her child for using a "pleasant" voice.

Or whisper your answer back. "You may have to whisper it several times, but your child will have to be quiet to hear you, and a lot of times he'll mimic your tone of voice," says Karen Shaffer, a mom of three in Highland, California.

By the time they're four, most kids are able to understand that their behavior has consequences. So you can start using the "I can't understand you when you whine" technique.

"When my children complain, I say, 'I'm sorry, but when you talk in that voice, I can't understand anything you're saying. Use your normal voice and I'll try to listen to you.' Then I ignore them until they start to comply," says Audrey Smith, a mom of two in Long Beach, California. It works, she says, but you have to be as consistent as possible.

And that's not easy, as we all know. Who among us hasn't caved in? Trouble is, if your child sees you can be broken, he'll simply up the ante, and your whining problem will be worse.

Besides being consistent, look for ways to reinforce the behavior you do want, like thanking him when he repeats his request in a polite tone.