Between March and June 2019, the SARS-CoV-2 virus broke out in Spain. The lockdown in response entailed the modification of certain habits in the infant–juvenile population, such as those related to the practice of physical activity and the implications derived from it. The aim of this study was to learn the impacts that lockdown had on manual dexterity in children aged 11–12 years. Methods: A total of 50 Spanish children aged 11–12 years (M = 11.40; SD = 0.50) participated, 33 (66%) boys and 17 (34%) girls. The Movement Assessment Battery for Children 2 (Movement ABC-2) and an ad hoc questionnaire for socio-demographic data and other relevant information were administered for the data collection. Results: There are significant differences (p < 0.05) in the results for the manual dexterity variables measured by the peg turning and line drawing tests as well as by the measured, scalar and percentile dimension scores for manual dexterity between before and after the lockdown in both boys and girls. No significant differences were found in measurements related to the triangle assembly variable (p = 0.125). Conclusions: A significant negative impact of SARS-CoV-2 lockdown on manual dexterity values was evident in boys and girls aged 11–12 years.