Objectives Mental chronometry is the scientific study of cognitive processing speed measured by reaction time (RT), which is the elapsed time between the onset of a stimulus and an individual’s response. This study aims at measuring the RT among young children with autism spectrum disorders (ASD) and comparing it with normal (typically developing) children. Methods 60 ASD children were selected from different ASD centers, and 60 normal children were selected from different kindergartens for participation in this study. Participants were aged 3–6 years old. The RT was measured using the Fitlight trainer device. The findings were statistically evaluated using independent t-tests and ANOVA tests. Result Significant differences (p < 0.0001) were found between both groups in all tasks, and ASD children demonstrated slower RT compared to the normal group. The RT measured through three senses (visual, auditory, and touch) for ASD and normal were 3.64 ± 2.16, 13.19 ± 2.41(trial), 1835.23 ± 757.95, 697.12 ± 87.83 (second), and 1550.89 ± 499.76, 752.67 ± 124.02 (second) respectively. Conclusion The evaluated RT showed significant impairment in RT among ASD in comparison to normal children and this was true for the three senses. The Fitlight trainer could be used to assess RT and stimulus-response among ASD children in various cognitive tasks. Similar studies, involving larger samples from different areas and involving other sense organs, are indicated to confirm the results.