Two remembering phenomenologies, vivid recollection and vague familiarity, have been extensively studied in adults using introspective self-report tasks, such as rememberknow. Because such tasks are beyond the capabilities of young children, there is no database on how these phenomenologies first develop and what factors affect them. In experiments with 5- to 14-year-olds, a child-appropriate behavioral methodology (conjoint recognition) was used to measure these phenomenologies. For both true and false memory, there were marked age increases in vivid recollective experiences, coupled with only slight increases in vague familiarity experiences. Thus, there is a vague-to-vivid developmental shift in the mental states that accompany remembering, a finding that is predicted by fuzzy-trace theory's explanation of recollection and familiarity.