The COVID-19 pandemic required in-person interventions to be adapted for remote delivery all over the globe. In South Africa, an in-person cascaded task-sharing naturalistic developmental behavioural intervention was adapted for telehealth delivery in a low-resource context. Here we describe the adaptations made (the ‘what’) and reasons for adaptations (the ‘why’). The Framework for Modification and Adaptations (FRAME) was used to document the ‘what’, and the Exploration, Preparation, Implementation, Sustainment (EPIS) framework to describe the ‘why’. Systematic member-checking ensured robustness of results. The ‘what’ included 10 adaptations: selecting WhatsApp as delivery platform, developing images with simple text to communicate intervention concepts, modifying session structure for hybrid delivery, including a caregiver self-reflection checklist, utilizing online practitioner training, supervision, assessment and consent procedures, developing session recording procedures, distributing session materials electronically, and developing caregiver–child interaction recording and uploading protocols. The ‘why’ included three outer contextual factors (the digital divide, WhatsApp security/privacy policy, and COVID-19 restrictions), three inner contextual factors (characteristics of caregivers and practitioners, ethics board guidance, and school leadership and organizational characteristics) and one innovation factor (support from intervention co-developers). Adaptations were made in response to unchangeable outer contextual factors and through identification of malleable inner contextual factors. Lay abstract We were busy with an early autism caregiver-coaching programme in South Africa, when COVID-19 stopped all in-person work. We changed the programme so it could be done using computers and/or phones. Here, we describe programme changes (which we call the ‘what’) and the reasons for those changes (which we call the ‘why’). We used a tool called the Framework for Modification and Adaptations (FRAME) to describe the ‘what’, and the Exploration, Preparation, Implementation, Sustainment (EPIS) framework to describe the ‘why’ of our programme changes. The team members who helped make these changes checked that the changes described were correct. We made 10 changes in total: we used WhatsApp to deliver the programme, made simple pictures with words as visual tools for the programme, changed some session activities, changed a self-reflection checklist, provided all activities online, changed the way assessment and consent was done, made a session recording guide, sent things needed for sessions by email and WhatsApp, and made a caregiver–child play recording guide. The reasons for changes (the ‘why’) were about factors outside schools (the types of phones and data people had, WhatsApp security rules, COVID-19 rules), things inside schools/workplace (about the caregivers and nonspecialists themselves, ethics boards, things about the school itself), and support from people who developed the programme. Changes were made by working with things inside schools/workplace that could change. Identifying what could change helped focus and guide which changes were made to a programme.