Do your teenagers’ behaviors mystify you? Are the changes you see breaking your heart? Parents mourn the loss of the wonder years when their kids become teens. “He was so creative and playful in elementary school.” “She was always laughing and had so many friends.” “He loved family time. Now he won’t come out of his room.” If you’re eager to know what caused your easy-going child to morphe into a sullen, irritable, and complicated person — this article’s for you.