Procedure: Before the pre-intervention assessments, the research team modified the car's seat and acceleration to the hand switch-driven, which allowed the car to be drivable for the child who met the inclusion criteria. Each child had a customized ride-on toy car in a hospital. After modifications, they received pre-intervention assessments, including behavioral videotaping and developmental assessments. The developmental assessments occurred at the first and last week of the 9-week intervention, and the end of the 9-week follow-up phase. A therapist who did not involve in the intervention and was blinded to the study purpose completed all the developmental tests. The driving and socialization behaviors were videotaped by the research team for 20 minutes/per session, one session/per week before, during and after the intervention phase at the child house or a hospital. All videotapes were coded by two independent coders, who were undergraduate students. Prior to making their ratings, the coder was instructed as to coding procedures by the PI, but he/she was not informed about the group assignment and the purpose of the study. Cohen's kappa coefficient was calculated between the two independent raters to establish good reliability before formal coding.