Background: Returning to work after childbirth is challenging for working mothers. The quality of childcare may have lifelong effects on children’s health, development and cognitive function. Over 60% of working women globally are informal workers without employment or maternity protections, but little is known about how these women care for their children. Methods: We conducted a mixed methods longitudinal cohort study among informal women workers in Kwazulu-Natal, South Africa between July 2018 and August 2019. Participants were followed up from late pregnancy until they had returned to work. We conducted structured quantitative interviews and in-depth qualitative interviews before and after the baby was born, and after returning to work. We then brought groups of participants together for a photovoice activity to explore the childcare environment. Thematic analysis was used to analyse qualitative data in NVIVO v12.4 and SPSSv26 was employed to analyse quantitative data. Results: Women returned to work soon after the baby was born, often earlier than planned, because of financial responsibilities to provide for the household and the new baby. Women had limited childcare choices and most preferred to leave their babies with family members at home, as the most convenient, low cost option. Otherwise, mothers chose paid carers or formal childcare. However, formal childcare was reported to be poor quality, unaffordable and not suited to needs of informal workers. Mothers expressed concern about carers’ reliability and the safety of the childcare environment. Flexibility of informal work allowed some mothers to adapt their work to care for their child themselves, but others were unable to arrange consistent childcare, sometimes leaving the child with unsuitable carers to avoid losing paid work. Mothers were frequently anxious about leaving the child but felt they had no choice as they needed to work. Conclusion: Mothers in informal work had limited childcare options and children were exposed to unsafe, poor-quality care. Maternity protection for informal workers would support these mothers to stay home longer to care for themselves, their family and their baby. Provision of good quality, affordable childcare would provide stability for mothers and give these vulnerable children the opportunity to thrive.