Observed 10-, 26-, and 42-month-olds playing under several distraction conditions to describe development of attention and distractibility. Found that casual attention decreased and focused attention increased with age. Ten-month-olds were more distractible than older children, even during focused attention. Infants were most distracted by the auditory-visual distractor, whereas oldest children were most distracted by the visual distractor. Results point to a developmental transition in processes underlying attention during play. (Author/KB)