It’s easy to make jokes about “preschool depression”—students get it every time the alarm rings—but finding depression, “relapses,” “chronicity,” and “treatment resistance” in 3-year-olds is not funny.

Researchers used to believe that “young children were too cognitively and emotionally immature to experience depressive effects,” says Joan L. Luby, M.D., but now believe they can and do suffer from Major Depressive Disorder (MDD).