Some children produce too much urine at night. These children may have low levels of a naturally occurring substance called vasopressin, which the brain normally produces during the night. Vasopressin reduces the amount of urine produced during the night and allows for uninterrupted sleep. This means that if the child has low levels of vasopressin at night, they may produce more urine than the bladder can hold. And if they do not wake up they may wet the bed.