Abstract Background Adolescents often experience their first encounter with alcohol at home, provided by parents who perceive it as a means of safeguarding their children against later alcohol-related issues. However, research shows that parental supply of alcohol is a risk factor for adolescent drinking. Notably, existing studies solely focused on parental supply during adolescence, neglecting the prospective evaluation of parental alcohol provision during early childhood on later alcohol use. Methods The data came from the Czech part of the European Longitudinal Study of Pregnancy and Childhood (ELSPAC), a longitudinal birth cohort study (N = 5,777). Mothers reported on the frequency of offering alcohol to children when children were 3, 5, 7, and 11 years old. The outcome was adolescent alcohol use at ages 15 and 18, reported by adolescents, mothers, and pediatricians. Control variables included sex, maternal education, family structure, and parental alcohol consumption. Results Three classes of children were identified based on parental alcohol supply: abstainers (75.5% of sample), infrequent sippers (16.2%), and frequent sippers (8.3%). Parental drinking increased the risk of both infrequent and frequent sipping. These classes were entered into two structural models (age 15 and age 18 alcohol use modeled as latent factors), alongside covariates. Compared to abstainer class, infrequent and frequent childhood sippers exhibited significantly higher alcohol consumption at age 15 (β = .21, p < .001; β = .25, p < .001, respectively) and age 18 (β = .11, p < .05; β = .24, p < .001, respectively). Conclusions This study represents the first prospective investigation quantifying early childhood alcohol exposure and its subsequent association with adolescent alcohol consumption. Findings emphasize the influence of family dynamics on alcohol behaviors, underscoring the necessity for targeted preventive measures, particularly within families with higher parental alcohol consumption. Key messages • Offering alcohol to children at ages 3-11, even infrequently, significantly increases the risk of more frequent drinking at ages 15 and 18, compared to those with no early exposure. • Parents who drink are more likely to have children who sip alcohol early, leading to higher alcohol consumption in adolescence. Prevention efforts should focus on family habits and early education.