This is the VOA Special English Health Report.

Many parents wish children were born with directions. Raising children is a complex job -- many would say the most complex there is.

So, from time to time, we are going to present information for parents. We will deal with subjects like diet and common childhood sickness. We will also talk about behavioral problems and other issues. And we will ask for questions to answer on the air.

Today we start with a common problem:bed-wetting. The American Academy of Pediatrics says about 40 percent of preschool-age children urinate in their sleep.

In most cases, childrenoutgrowit. The academy says 20 percent of five-year-olds and ten percent of six-year-olds wet their bed. By the age of twelve, that number drops to three percent.

The National Institutes of Health says experts are not sure what causes bed-wetting. The most likely causes, the experts say, include slower physical development and overproduction of urine at night.

Smallerbladdersfill more quickly. And some bodies take longer to develop the warning system between the brain and the bladder. Some children may not receive the message to wake up when they need to urinate.

Urologic and kidney experts at the National Institutes of Health also say some children may not produce enough antidiuretic hormone. The body usually produces more of this hormone at night so less urine is produced during sleep. The bladders of children who produce lesser amounts of antidiuretic hormone are more likely to fill up while they sleep.

Experts say feeling nervous and worried can sometimes lead children to wet the bed. Genetics may also play a part. Researchers say some family genes appear to be involved in bed-wetting.

Children sometimes think they are bad because they wet the bed. Parents may get angry. Or they may feel guilty, like they have done something wrong. Doctors say it is important to know that how a parent reacts could affect a child's self-image. We will talk more about the subject of bed-wetting next week. We will talk about different ways that doctors suggest to deal with it.

And that's the VOA Special English Health Report, written by Caty Weaver. You can download MP3 files and transcripts of our reports at voaspecialenglish.com. And to send us questions, write to special@voanews.com. Please be sure to include your name and where you are writing from. I'm Mario Ritter.

bed-wetting  : 尿床

outgrow  : to lose or discard in the course of maturation（在成熟过程中逐渐失去）

bladder  : 膀胱