Social workers were heavily impacted by the COVID-19 pandemic. In this study, we examined the well-being, burnout and work conditions of UK children’s social workers at five time points of the COVID-19 pandemic. This was a cross-sectional mixed methods study analysing data from 1,621 social workers who worked in children’s services in the UK in 2020–2022. Data were collected using anonymous online surveys which included both quantitative and qualitative questions. The mental well-being of participants decreased as the pandemic progressed and work-related burnout increased. In the later stages of the pandemic, children’s social workers in Northern Ireland fared better than their Great Britain counterparts in relation to their well-being and levels of burnout. Thematic analysis of qualitative data revealed four major themes: Changes in service demand and referrals, Adapted ways of working, Staff shortages and Emotional impact. The findings highlight the challenges that the children’s social workers encountered during the COVID-19 pandemic and have implications for policy, practice and research.