About one in every five children will experience depression before adulthood. Once a young person has had an episode of major depression, he or she is at risk of developing depression again within the next five years. This young person is also at risk of other mental health problems. Teen depression and adult depression are different illnesses due to the developmental issues that teenagers face. Teenagers experience depression differently, and they may show different symptoms. However, if your teenager is showing four or more symptoms of depression for longer than two weeks, he or she may be suffering from teen depression.