Free classification in children.
D000367:Age Factors; D002648:Child; D002657:Child Development; D002675:Child, Preschool; D003118:Color Perception; D003210:Concept Formation; D004192:Discrimination, Psychological; D005556:Form Perception; D006801:Humans; D008297:Male; D012054:Reinforcement, Psychology; D012718:Set, Psychology; D012858:Size Perception