INTRODUCTION Children and adolescents use different markers to elaborate the concept of time, and such markers change along their development. The objective of the present article was to analyze changes in time concepts in different age groups. METHODS The study included 81 children and adolescents aged 6 to 17 years, attending elementary or high school at a public school in southern Brazil. Participants were asked to provide their definition of time, either orally (children) or in writing (older children and adolescents). RESULTS Twenty-one words were identified as related with the definition of time. The term "hours" was the most frequently cited (24.7%), followed by "clock" and "family" (11.1% each). Among children aged 6 to 8 years, "family" was the term most frequently mentioned to refer to time. Between 9 to 11 years of age, the notion of time was essentially related to the use of a clock, and in the 12-17-year age group, time was mostly associated with the word "days." The word "family" appears to be a frequent temporal marker in childhood, but loses this function during adolescence, as new social relationships are established. CONCLUSION The results of this study show that the concept of time varies according to age. Chronobiological studies should therefore take into consideration the temporal perception peculiar to each age group.