When Adrianna and Jermaine Hannon's second child, Jayden, was 14 months old, the California couple began to worry that something was wrong. The child became preoccupied with toy cars, turning them over and rolling their wheels ceaselessly at an age when most other toddlers flit from one activity to another. Jayden would also line up cars, magazines or blocks on the floor or a table in as straight a line as he could make, never stacking objects as other kids would.