Even though the new school year is in full swing, kids still have plenty of time to play outside in the sunshine before dinner.

Yet as the sun starts to set earlier each night and daylight savings time ends in November, a sneaky form of depression called seasonal affective disorder, or SAD, can become a problem for some children.

Left untreated, kids with SAD may be prone to depression throughout their lives. Even more troubling is that experts say many children with SAD aren’t being diagnosed.

The good news is that if you know the risk factors and the symptoms, and where to turn for treatment, you can help your child feel better.

What is seasonal affective disorder?

Seasonal affective disorder (SAD), or what is now called major depressive disorder recurrent with seasonal pattern, is a form of depression that affects both adults and children. Unlike depressive episodes that can happen at any time of the year, SAD is one that returns each year, usually during the fall and winter months, said Dr. Adelle Cadieux, a child psychologist at Helen DeVos Children’s Hospital in Grand Rapids, Mich.

Approximately 3 percent of kids ages 9 to 17 have SAD, according to Dr. Norman E. Rosenthal, a world-renowned psychiatrist based in Rockville, Maryland and author of “Winter Blues: Everything You Need to Know to Beat Seasonal Affective Disorder.”