Child health programmes in the United Kingdom offer every child and their family an evidence-based programme to support child health and development. During the COVID-19 pandemic, health visiting services in many areas were reduced to a partial service, with significant variability between and within the four United Kingdom countries. This study investigated the impact of the pandemic on health visiting services and developed recommendations for policy and practice. Conduct a realist review of relevant literature. Engage with key stakeholders in policy, practice and research across the United Kingdom. Identify recommendations for improving the organisation and delivery of health visiting services, with a focus on services being equitable, effective and efficient. The realist review followed Pawson's five iterative steps and involved key stakeholder representatives at every step. We searched five electronic databases and references of included articles, as well as relevant organisational websites, to find quantitative, qualitative, mixed-methods and grey literature related to health visiting services in the United Kingdom during the COVID-19 pandemic. An assessment of their relevance to our initial programme theory determined inclusion in the review. Data were extracted, organised and presented as draft context, mechanism and outcome configurations. These were iteratively refined through meetings with 6 people with lived experience of caring for babies during the pandemic and 23 professional stakeholders. Context, mechanism and outcome configurations were then translated into findings and recommendations. One hundred and eighteen documents contributed to the review and collectively revealed the far-reaching, uneven and enduring impact of the COVID-19 pandemic on babies and families. Data uncovered significant concerns of families and practitioners amidst the pandemic, along with the service's corresponding actions. These concerns and responses underscored the critical importance of fostering and sustaining trusting relationships between health visitors and families, as well as conducting holistic assessments for early intervention. Although we found minimal evidence of decision-making within organisational/managerial levels, the data illustrated the diverse and complex nature of health visiting work and the need for flexibility and resourcefulness. The primary limitation of this review was a lack of specific evidence from the United Kingdom nations other than England. There was also a lack of data focusing on changes during the COVID-19 pandemic at a local management level. The needs of babies, children and families, and the delivery of services to support them, were not prioritised in the early phase of the pandemic response. Our data show that the health visiting service was concerned with maintaining visibility of all children, and especially supporting families with a new baby. Health visiting services adapted in numerous ways to respond to these concerns. Implications for policy and practice are presented, identified from our analysis and discussions with stakeholders. The RReHOPE study is part of a jigsaw of evidence, which will provide a much stronger evidence base for future policy and practice. This realist review presents several areas for future research, including how health visiting is organised at local management level; how to optimise limited resources; factors affecting differing uptake in different regions; and analysis of the effectiveness of health visiting using large cohort studies. This article presents independent research funded by the National Institute for Health and Care Research (NIHR) Health and Social Care Delivery Research programme under award number NIHR134986.