This study addresses the scarcity of longitudinal research on the influence of screen media on children. It aims to explore the longitudinal relationship between children's vocabulary development and their exposure to screen media. The study, initiated in 2017, included 72 children (37 boys) in Östergötland, Sweden, at three key developmental stages: preverbal (9.7 months), early verbal (25.5 months) and preliterate (5.4 years). Parents completed online surveys at each time point, reporting their child's screen time. At 10 months and 2 years, age-appropriate vocabulary assessments were conducted online. At age 5, children's vocabulary was laboratory assessed. Correlational analysis revealed a negative relationship between language scores and screen media use across all time points. Furthermore, a cross-lagged panel model demonstrated that screen media use showed significant continuity over time, with screen use at age 2 predicting language development at ages 2 and 5. This longitudinal study, spanned from 9 months to 5 years of age, established a predictive negative association between children's exposure to screen media and their vocabulary development. These findings underscore the need to consider the impact of screen media on early childhood development and may inform guidelines for screen media use in young children.