Funding for this research was provided by:
Medical Research Council (Block grant)
Received: 13 November 2019
Accepted: 15 June 2020
First Online: 22 June 2020
Ethics approval and consent to participate
: The study was approved by Wales Research Ethics Committee 5 (Bangor), Health and Care Research Wales. Reference number 16/WA/0187. Parents of all participants provided written consent for the study.
: Not applicable.
: The authors declare that they have no competing interests.