The first step: "If you're really worried  -- particularly about your child's breathing or a drastic change in his behavior  -- go directly to the ER," says Marc Gorelick, M.D., medical director of the Emergency Department at Children's Hospital of Wisconsin in Milwaukee. What else you need to know about some of the scariest childhood emergencies:

Febrile seizures
A response to fever by a young child's immature brain, febrile seizures typically occur between the ages of 6 months and 5 years in 2 to 5 percent of all children. They come on suddenly, with no early warning signs.

Fortunately, there is no long-term cognitive or behavioral damage. "Febrile seizures generally require urgent evaluation but almost always have a benign outcome," says Kathy Shaw, M.D., chief of emergency medicine at Children's Hospital of Philadelphia. Most are "simple," meaning they last less than 10 or 15 minutes and don't recur within 24 hours. Typically, a child is evaluated and released, and is fine.

But in a small number of these cases, children with febrile seizures have something more serious, such as meningitis (see the next section). And some have "complex" seizures  -- longer than 15 minutes or recurring within the day  -- which might indicate epilepsy. (However, a simple febrile seizure can never "bring on" epilepsy.)

You can't really prevent febrile seizures. Most often, a fever of 103°F or higher sets one off. Even giving your child a fever reducer at the first sign of a temperature won't prevent one.

If a febrile seizure occurs once in a child over 18 months, there's a 30 percent chance it'll happen again. It's even more likely if these seizures run in your family, if your baby was 18 months or younger the first time, or if it was triggered by a milder fever, such as 101°.

So be prepared. If it's a first-ever seizure, call 911, but don't try to take her to the ER yourself while she's having one. Instead, without restraining her, lay her down on her back on a rug so she won't fall or bang her head against something hard. Gently turn her head to the side to prevent choking (don't put anything in her mouth, including medicine). Cool her down (unbutton her clothes, use a cool cloth). After it's over, let her sleep and then take her to the ER.

If it's a second seizure and the first one was simple, there's no need to call 911 (unless it lasts more than five minutes). When it's over, call your pediatrician. If it's off hours, go to the ER for an evaluation.

Laurie Tarkan, a frequent contributor on health topics for The New York Times, is writing a book on pregnancy. She's a mom of two in Maplewood, NJ.