Genetics plays a clear role in bedwetting. If one or both parents were bedwetters there is a much higher likelihood the child will also have this issue. It is not unusual to find relatives who struggled with bedwetting as children.
Children who wet their beds are deep sleepers and the communication between their bladder and their brain is not strong enough to wake them. Studies show that these children are difficult to wake up.
Bedwetting children tend to produce larger amounts of urine at nighttime versus other children. This can result in the bed being completely soaked just a couple of hours after going to bed and/or bedwetting episodes several times every night. These children often do not produce as much of an antidiuretic hormone as non-bedwetters.
Some bedwetting children may have overactive bladders that contract more easily with less control, and therefore cannot hold as much urine. There is evidence that children who do not respond to specific medication that reduces urine production tend to have smaller than normal bladder capacity. As a child grows, the bladder also grows, which is one of the factors that helps children outgrow bedwetting.
There may be a relationship between chronic constipation and bedwetting. Treatment of constipation may help some children with bedwetting. A bowel that is full will put pressure on the bladder, which reduces the amount of urine the bladder can hold.