My 4 year son is fully potty trained during the day but at nite he needs a diaper. is this normal?

Children often gain daytime bladder control before nighttime issues are conquered. Approximately 1-in-9 children at age 4 will still have nighttime wetting. This percentage decreases by approximately 15% a year, as children age and mature. Nocturnal enuresis is an involuntary release of urine most often caused by a bladder that has not yet developed sufficiently, so it is not your child’s fault nor your fault as a parent. It is simply a question of growth and development. For more information you might check out the articles under the Bedwetting Education tab, specifically, “The Top 10 Reasons Why It's OK That Your Child Wets the Bed (Really!).”