Typically by age 6.
Bed wetting is frustrating for child and parent. As a parent, be aware that bed wetting is actually a very normal part of childhood. Nearly 50% of 3-year-olds and 40% of 4-year-olds wet the bed several times in a week. A quarter of 5-year-olds and nearly 15% of 6-year-olds wet the bed, at least occasionally. You need only consult a doctor if bed wetting continues past the age of 6 or 7, or if your child suddenly starts wetting the bed after a long, steady period of staying dry at night. Sudden changes from dry to wet could indicate a medical problem.
The reasons for bed wetting are biological and will change with age. Until they are close to school age, most children have just not developed enough bladder control to keep them from wetting the bed. There are steps you can take to help your kids. Limit liquids before bed. Make a few trips to the bathroom before bed. Do not make the child feel guilty. Leave a light on and encourage nighttime bathroom visits. Lastly, use a mattress cover instead of training pants, because diapers and “pull-ups” can prevent children from learning when they are urinating.