I knew I was being watched. Dark eyes tracked my movements, intent. Impulsively, I grinned widely. I picked up a stuffed elephant from the menagerie on the coverlet and hugged and kissed it. Her eyes widened slightly as my baby daughter registered the idea. Today she is six years old, and “Ellie” is still her favorite plush companion when she needs a cuddle and mommy is not immediately available.

As the articles in this special issue underscore, a child’s rapid cognitive development begins from the earliest ages and may continue into young adulthood. Before they can talk, tots are learning how the world works and how they can apply that knowledge. “Test Subjects in Diapers,” by Gisa Aschersleben, reveals how quickly infants learn to think critically—and the ways in which scientists can “ask” babbling babies to show what they know; turn to page 10.

Knowledge about a child’s rapid mental development also serves to emphasize the importance of early intervention in cases where children have special needs. Articles in the issue explore faster detection of disorders and possible therapies for children with autism (page 14), ADHD (page 36) and Down syndrome (page 42).

When does the brain finish “growing up”? Many neuroscientists say that cognitive development, especially in areas of the brain that are associated with decision making and other “executive” functions, continues into the second decade of life, reports Leslie Sabbagh in “The Teen Brain, Hard at Work,” beginning on page 54. Meanwhile psychologist Robert Epstein warns against excess reductionism in applying imaging studies of teen and adult brains to complex human behaviors. We blame teen turmoil on immature brains—but, he asks, did the brains cause the turmoil, or did the turmoil affect the brains? His article, “The Myth of the Teen Brain,” starts on page 68.

As you page through the articles in the issue, we hope one thing will be clear: as we learn more about how the mind operates, we are better able to help children grow up to lead happy, fulfilling lives.

Executive Editor editors@sciam.com