Fetus stage
When the fetus is only 14 weeks old, the kidneys already start to produce urine. In the beginning, the amniotic fluid contains more or less only urine.
The bladder is emptied very irregularly and is never completely emptied.
Infants
A newborn child urinates regularly, about once an hour. The bladder is still not emptied completely, but the child releases all the urine its body needs to get rid of.
Small children
From about two years of age, your child becomes interested in going to the toilet and wanting to go there to pee. Your child can control his/her bladder to a certain extent, but has trouble holding water on demand, that is waiting. Your child also has problems peeing on demand. When he/she feels the need to pee, he/she will want to go to the toilet right away.
By the age of 4 most children can control their bladders. This means that they can wait a short while before going to the toilet and that they can empty their bladders on demand, for example "Go and pee now, and then we're going to the store".
Preschool children
By the age of 6, 90% of all children keep dry both day and night. On the other hand, this means that one child in ten still has problems controlling his/her bladder by the time he/she starts school. They have problems holding water and need to go to the toilet immediately once the bladder starts signalling.