Non ELI 5 version from Up to Date During the first three years of life , bladder storage capacity increases disproportionately relative to body surface area . By four years of age , most children void five to six times per day . Development of bladder control appears to be a progressive maturation whereby the child first becomes aware of bladder filling , then develops the ability to suppress detrusor contractions voluntarily and , finally , learns to coordinate sphincter and detrusor function . These skills usually are achieved , at least during the day , by approximately four years of age . Nighttime bladder control is achieved months to years after daytime control , but is not expected until five to seven years of age More ELI 5 version Basically it ' s a combination of having disproportionate bladder sizes and not enough brain control to hold the flood gates back . Edit to add This is generalized . Obviously every body is different . Don ' t ask me if it ' s pathological that youyour friend still pees the bed into adulthood and beyond . Instead I urge you to bring this up to your doctors ! They ' re there to help you and they can determine whether there is an underlying pathological cause much better than anyone over the internet . Best of wishes . Stay dry .