Purpose <p>Little is known about the association between low- and no-calorie sweetened (LCS) product consumption and children’s dietary quality, despite the promotion of these products as sugar alternatives. This study examines the trends and associations between LCS product consumption and intakes of free sugar, ultra-processed food and beverages (UPFB), and other key dietary components among UK children.</p> Methods <p>Repeated annual cross-sectional data from the National Diet and Nutrition Survey (2008/09-2018/19) for children aged 4–18 years (<i>N</i> = 5,922) were analysed. Children were categorized into No-LCS (0%g/day), Low-LCS (≤ 6.8%g/day), Mid-LCS (6.9–17.4%g/day), and High-LCS (≥ 17.4%g/day) groups based on a four-day food diary. The trends and associations were assessed using multivariable linear regression models, adjusted for sociodemographic factors.</p> Results <p>In 2008/09, the High-LCS group had lower free sugar intake (-1.9%kcal_total/day; 95% CI: -2.8, -1.0) compared with the No-LCS group. Over 11 years, free sugar intake declined in all groups, with similar declines observed across the LCS groups. By 2018/19, no difference in free sugar intake was observed between the High-LCS and No-LCS groups. Moreover, consumption of UPFB decreased (-0.8%g_total/day per year; 95%CI: -1.1, -0.6) while water increased (2.7%g_drink/day per year; 95%CI: 2.2, 3.1) in the No-LCS group over 11 years. Similar changes were observed in other LCS groups but were less pronounced in the High-LCS (vs. No-LCS) group.</p> Conclusions <p>LCS product consumption was not consistently associated with lower free sugar intake among UK children. Differences in intakes of ultra-processed foods and water highlight the importance of considering dietary patterns beyond individual nutrients.</p>