Although COVID-19 is no longer classified as a pandemic, its serious impact on human health, particularly among children in China, remains profound due to the country's lengthy and highly restrictive zero-tolerance policy. This study aims to explore the potential influence of COVID-19 on the growth of preschool children.The participants of the study were preschool children identified in 2018, forming the baseline cohort. We systematically monitored their routine physical examination data over the following three years-2019, 2020, and 2021. Data on dependent variables such as median differences, growth levels, and nutritional status assessments were collected. Specifically, we selected 3-year-old children from the 2018 cohort and followed them for four years, analyzing paired data from 2018 to 2021 to assess the impact of COVID-19 lockdown measures on their growth. Tracking the same cohort over time with paired data reduces intergroup biases caused by variations in participants.The results of the study indicate that the major lockdown during the COVID-19 pandemic did not hinder height growth; in fact, it slightly promoted it among preschool children. However, the lockdown also accelerated weight gain, and the changes in both height and weight led to variations in BMI.We conclude that the prevalence of children with overweight and obesity during the lockdown period was significantly higher compared to pre-pandemic levels, suggesting that lockdown measures exacerbated these conditions. Moreover, these negative effects are likely to persist in the long term.© 2025. The Author(s), under exclusive licence to Springer Nature Limited.