Credits: Brain Scans, Figure 1 from: Knickmeyer et al., 2008; Real People: Toddler in orange hat: Jani Bryson/Thinkstock; Small child, Jaroslaw Wojcik/Getty Images; Baby boy (12–15 months) close-up, portrait, Photodisc/Getty Images; Baby boy eating, © sanapadh/Alamy; Baby learning to stand assisted by a stool, Aseph/Shutterstock; Little boy playing with colorful cubes, Sergiy Bykhunenko/Shutterstock