Abstract Background The intense childrearing years often coincide with the heightened work demands and responsibilities of the career-building years. We aimed to evaluate the association between family-life stage and men’s and women’s experience of work and private demands, and the conflict between these demands. Methods We evaluated 3532 mothers and 731 fathers as part of the Portuguese population-based birth cohort Generation XXI (2018-2020). Data on family-life stage (exposure), work demands, private demands, and work-to-family conflict (outcomes) were retrieved at the 13-year follow-up wave, as well as data on sociodemographic and household characteristics. Family-life stage was operationalized according to the age of the youngest child: stage 1 (≤5 years), stage 2 (6-11 years), and stage 3 (≥12 years). Ordinal logistic regression models were used to estimate associations. Results Men reported more frequently long working hours, while women spent more time on household and child-related tasks. After adjustment for parents’ and household characteristics, mothers and fathers with younger children were more likely to report spending more time on child-related tasks (ORmothers = 1.83; 95%CI 1.44, 2.33; ORfathers = 2.36; 95%CI 1.41, 3.94), compared to those with older children. Fathers with younger children were also more likely to report spending more time on household tasks (OR = 2.20; 95%CI 1.30, 3.73 for routine tasks and OR = 1.75; 95%CI 1.03, 2.97 for sporadic tasks). Mothers exhibited a significant association between family-life stage and time-based work-to-family conflict when they had younger children (OR = 1.24; 95% CI 1.05, 1.47 for family-life stage 2 and OR = 1.28; 95% CI 1.00, 1.63 for family-life stage 1). Conclusions Both fathers and mothers with young children experienced increased private demands, but only mothers experienced work-to-family conflict. This reveals that family and working arrangements remain marked by a gendered pattern against women.