Is Adolescents’ Free Sugar Intake Associated with the Free Sugar Intake of Their Parents?

High free sugar intake can lead to increased dental caries, obesity, and other health risks among adolescents. Studies have shown that family factors, especially parents, are one of the primary factors influencing adolescents’ sugar intake. This study aims to investigate the influence of adolescent parents’ free sugar intake, knowledge, attitude, and practice (KAP) on adolescents’ free sugar intake. A total of 1090 pairs of adolescents and their parents from 10 secondary schools in Changsha were enrolled in a cross-sectional study. Free sugar intakes of parents and adolescents were measured using the food frequency questionnaire (FFQ). The current status of parents’ knowledge, attitude, and practice in consuming free sugar was investigated using online and offline questionnaires. Parental free sugar intake was 11.55 (5.08, 21.95) g/d, and that of adolescents was 41.13 (19.06, 80.58) g/d. Parental free sugar intake, free sugar knowledge level, intake behavior, and guidance behavior were associated with adolescent free sugar intake. A superior level of parental free sugar knowledge (adjusted OR = 0.726, 95% CI: 0.557~0.946) was a protective factor for adolescent free sugar intake. Moderate and high levels of parental free sugar intake (adjusted OR = 1.706, 95% CI: 1.212~2.401; adjusted OR = 2.372, 95% CI: 1.492~3.773, respectively) were risk factors for free sugar intake in adolescents. Given the importance of parental influence on the adolescent free sugar intake, further limiting parental intake and increasing awareness of free sugars could play an active role in future interventions for adolescents’ free sugar intake.