Rain lashes against the clinic windows on a busy autumn morning. The waiting room has been packed since opening, and you grab a quick glance at the next chart before stepping into the room.

You walk in to find your next patient, 18-month-old Leo. He is sitting on the linoleum floor, intently spinning the wheels of a small toy car. “Hey there, Leo!” you say cheerfully, but he doesn’t look up or acknowledge your entrance.