Theories of language acquisition suggest that primary school constitutes a pivotal source of majority-language exposure, which is particularly important for bilingual children. During the periods of school closures caused by the COVID-19 pandemic, this source of language input was reduced or even entirely unavailable for several months, raising the question of how the language competences of mono- and bilingual children developed during this time. This study examines the German receptive vocabulary development of mono- and bilingual primary school children in Germany at the time of the COVID-19 school closures, using data from the Newborn Cohort of the German National Educational Panel Study from 2015 to 2021. Contrary to the theoretical expectation of exacerbated educational disparities, our findings reveal no significant widening of the existing vocabulary gap between mono- and bilingual children during the pandemic. Despite the potential for reduced German language exposure, particularly among bilingual children, vocabulary trajectories remained surprisingly stable in both groups, with bilingual children even showing signs of a slight but significant catch-up effect. Additional analyses to examine potential growing vocabulary gaps by migration background or parental education yielded no evidence of a widening achievement gap in vocabulary. These findings may be attributed to the well-documented stability of receptive vocabulary, as well as to various other factors outlined in the discussion. Our study contributes to the body of differentiated research on educational impacts of the pandemic and highlights the importance of careful examination regarding the relationship between school and competence development in the context of social inequalities.