Climate change is the number one threat to child health according to the World Health Organisation. It increases existing inequalities, and lower-income countries are disproportionately affected. This is unjust. Higher-income countries have contributed and continue to contribute more to climate change than lower-income countries. This has been recognised by the United Nations Committee on the Rights of the Child, which has ruled that states can be held responsible if their carbon emissions harm child rights both within and outside their jurisdiction. Nevertheless, there are few analyses of the bilateral relationship between higher- and lower-income countries concerning climate change. This article uses the UK and Malawi as a case study to illustrate higher-income countries’ impact on child health in lower-income countries. It aims to assist higher-income countries in developing more targeted policies. Children in Malawi can expect more food insecurity and reduced access to clean water, sanitation, and education. They will be more exposed to heat stress, droughts, floods, air pollution and life-threatening diseases, such as malaria. In 2019, 5,000 Malawian children died from air pollution (17% of under-five deaths). The UK needs to pay its ‘fair share’ of climate finance and ensure adaptation is prioritised for lower-income countries. It can advocate for more equitable and transparent allocation of climate finance to support the most vulnerable countries. Additionally, the UK can act domestically to curtail revenue losses in Malawi and other lower-income countries, which would free up resources for adaptation. In terms of mitigation, the UK must increase its nationally determined commitments by 58% to reach net zero and include overseas emissions. Land use, heating systems and renewable energy must be reviewed. It must mandate comprehensive scope three emission reporting for companies to include impacts along their value chain, and support businesses, multinational corporations, and banks to reach net zero.