Objective: The aim was to compare dietary patterns and nutritional status of medium-marginalized schoolchildren in Hermosillo, Mexico, pre- and post-pandemic. --- Materials and Methods: Diet of 100 schoolchildren pre-pandemic and 100 post-pandemic were evaluated using 24-hour recalls. Principal components analysis was performed to identify dietary patterns. Anthropometric measurements were taken to calculate Z BMI-for-age. In the post-pandemic period, labels of ultra-processed foods were analyzed to identify sweeteners. --- Results: Prevalence of overweight and obesity increased (p < 0.05) from 37% pre-pandemic to 54% post-pandemic, along with energy intake (1610 to 1816 kcal/d). There were 3 dietary patterns: Ultra-processed, Healthy, and Poor. Proportions of children in each pattern were comparable pre-pandemic, but the Poor pattern increased (p < 0.05) post-pandemic (34% vs. 42%). Protein intake was lower in children in the Ultra-processed pattern pre-pandemic, but post-pandemic, protein and fat intake were lower in children in the Poor pattern, increasing (p < 0.05) their overweight and obesity prevalence (9% vs. 21%). The most consumed ultra-processed products included 36 types of sweetened beverages, 33 types of candy, 20 different types of chips, and 15 varieties of cookies, most of which contained non-caloric sweeteners such as acesulfame K, aspartame, and sucralose. --- Conclusions: The pandemic reduced the diet quality and increased the prevalence of overweight and obesity in medium-marginalized schoolchildren in Northwest Mexico, with high consumption of ultra-processed foods containing non-caloric sweeteners Key words: Dietary patterns, schoolchildren, nutritional status, ultra-processed food.