It says explain it like I ' m five so I will . Short answer immaturity of pathways in the central nervous system . Long answer At the beginning of life we don ' t have voluntary control of our sphincters , the ring shaped muscles that allow or deny the expulsion of urine or excrement . When we acquire control varies but usually happens between 2 and 4 years of age . Nocturnal control also involves the ability to wake up and regain control of the body . When we are asleep and are dreaming motor activity is blocked from the rest of the body to avoid acting out the dream . If this doesn ' t happen you get a sleep walker . If you wake up but the block doesn ' t go away you may be semi conscious but can ' t move . A lot of these usually go away within a normal time frame but there are teens that the signal to wake up is not sent still and have to be woken up or they will wet the bed . It ' s not laziness it ' s that the center or nucleus in the central nervous system hasn ' t quite matured yet .