Time processing difficulties are associated with developmental disorders. Questionnaires for assessing children's sense of time are available from primary school, but we lack valid proxy-report tools for younger children, who are not able to complete self-reports. This study aimed to assess the criterion validity of a questionnaire investigating preschoolers' sense of time from the points of view of their parents and teachers. One hundred seventy preschoolers were included in the sample. Their parents and teachers completed the Sense of Time Questionnaire, and the children were administered time reproduction and time discrimination tasks, both concurrently and 7 months later. The assessment of preschoolers' sense of time reported by teachers, but not by parents, predicted the children's time processing skills both concurrently and longitudinally. The teacher version of the Sense of Time Questionnaire constitutes a valid instrument for assessing and predicting preschoolers' time processing skills and can be used for clinical and research purposes STATEMENT OF CONTRIBUTION: What is already known on this subject? Time processing difficulties are associated with developmental disorders such as ADHD and dyscalculia. Early assessment of time processing skills is important for clinical (e.g., screening) and research purposes. We do not have valid questionnaires for assessing sense of time in young children. What the present study adds? The sense of time ability reported by teachers predicts preschoolers' time processing skills. The sense of time ability reported by parents does not predicts preschoolers' time processing skills. The Sense of Time Questionnaire is a valid instrument for investigating time processing skills of 4-6 aged children.