Multiple levels of category inclusiveness in 4 object domains (animals, vehicles, fruit, and furniture) were examined using a sequential touching procedure and assessed in both individual and group analyses in eighty 12-, 18-, 24-, and 30-month-olds. The roles of stimulus discriminability and child motor development, fatigue, and actions were also investigated. More inclusive levels of categorization systematically emerged before less inclusive levels, and a consistent advantage for categorizing high versus low perceptual contrasts was found. Group and individual analyses generally converged, but individual analyses added information about child categorization over group analyses. The development of object categorization in young children is discussed in light of efficiency of processing and similarity-differentiation theories. (Contains 3 tables and 1 figure.)