Children don't wet the bed on purpose, or because they're too lazy to get up and use the toilet. Even children who have been successfully potty-trained may still wet the bed occasionally up to the age of 10. You should seek medical advice only if your child is aged six or older and wets the bed more than once a week. There may be a medical reason.

Studies of children's brainwaves show that there is a physical reason why some children wet the bed (the medical term is nocturnal enuresis). A new study, conducted at the University of Mersin and reported in the October issue of the Journal of Childhood Neurology, suggests that children with nocturnal enuresis have delayed brain maturation.

The study measured resting brain activity using EEGs and found that children aged six to 14 who wet the bed have high levels of delta waves during sleep. All children have high delta-wave activity during sleep up to the age of two, but usually this lessens as the child matures. Compared with other children, those who wet the bed also had less alpha-wave activity, which usually increases as a child ages. The differences in the activities of delta and alpha waves suggest that the brains of bedwetters are developing more slowly.

Recent studies have also found that some children who wet the bed lack a normal increase in antidiuretic hormone (ADH), which controls urine production at night.

If you have a bedwetting child, it's best to buy a plastic cover for the mattress, keep extra sheets on hand. Stay calm and loving, because scolding and impatience could damage your child's self-esteem.

Bedwetting runs in families, so think back and you may recall that your parents also had a lot of sheet-changing to do.

Patient and supportive parents will find that the condition eventually clears up on its own. Until then, encourage your child to use the toilet before bed. Never wake your child to use the toilet - it's disruptive and won't solve the problem.