Background: Mealtime television use has been cross-sectionally associated with suboptimal diets in children. This study aimed to assess the two-year prospective association between baseline mealtime television use and subsequent diets in young children, and identify socioeconomic differences. Methods: Parents reported their child’s television use at meals, and fruit, vegetable, and discretionary food intakes. Multivariable linear and logistic regression analyses assessed the association between baseline mealtime television use and follow-up diet outcomes. Differences were assessed by socioeconomic position. Results: Participants were 352 Australian parents of children aged six months to six years. Daily mealtime television use (average frequency/day) was associated with higher daily frequency of discretionary food intakes (β 0.2, 95% confidence interval (CI) 0.07–0.67) at the 2-year follow-up. Individually, television use during breakfast and dinner (1–2 days/week compared to never) predicted higher daily intake frequency of discretionary food, β 0.36 (95% CI 0.12–0.60) and β 0.19 (95% CI 0.00–0.39), respectively. Similarly, 3–7 days/week of television use during breakfast and lunch predicted higher frequency of discretionary food intake, β 0.18 (95% CI 0.02–0.37) and β 0.31 (95% CI 0.07–0.55), respectively. Associations were not socioeconomically patterned. Conclusions: Investigating mealtime television use motivators across the socioeconomic spectrum could inform interventions targeting the high consumption of discretionary foods in children.