Examined in 4 experiments 2-year-olds' knowledge of solidity in search tasks. Found no evidence that 2-year-olds represented solidity and support constraints on trajectories of falling objects; two experiments included 2.5-year-olds who succeeded on search tasks. Explored implications of 2-year-olds' poor performance in light of very young infants' success on looking- time measures of sensitivity to similar constraints on object motion. (Author/KB)