Funding for this research was provided by:
National Health and Medical Research Council (APP1070571)
South African National Research Foundation (CPRR13090934186)
University of Cape Town Research Committee (NA)
DST-NRF Centre of Excellence in Human Development (NA)
Received: 18 March 2020
Accepted: 8 March 2021
First Online: 23 March 2021
: All parents were provided with written information about the study and gave written informed consent for their children to take part in this study. Ethical approval was obtained from the University of Cape Town Human Research Ethics Committee (HREC Ref. No.: 237/2012), the University of the Witwatersrand Human Research Ethics Committee (Medical) (M140250), and the Mpumalanga Provincial Departments of Health and Education.
: Not applicable.
: CD is a member of the editorial board for BMC Public Health. The other authors declare that they have no competing interests.