This study investigates the on-line processing of scrambled sentences in Japanese by preschool children and adults using a combination of self-paced listening and speeded picture selection tasks. The effects of a filler-gap dependency, reversibility, and case markers were examined. The results show that both children and adults had difficulty in comprehending scrambled sentences when they were provided as reversible sentences. The reversibility effect was significant for children, whereas the interaction of reversibility and a filler-gap dependency was significant for adults. However, this does not indicate that children's parsing is fundamentally different from that of adults. For those children who processed the nominative and accusative case markers equally fast, the reactivation of the dislocated constituent was observed in the gap position. These results suggest that children's processing is basically the same as adults' in that their sentence processing is incremental and they parse a gap to form a filler-gap dependency.