Received: 19 June 2020
Accepted: 16 October 2020
First Online: 28 October 2020
Ethics approval and consent to participate
: The Regional Committee for Medical and Health Research Ethics (REC) in Norway, approved the study in the autumn of 2012, study number 2012/1460. Ethical principles from the Declaration of Helsinki were followed throughout the process.
: Informed written consent was obtained from all participants and their respective parents or guardians.
: Parents or guardians of the study participants gave written consent for their respective children's personal details along with any identifying images to be published in this study.
: The authors Siv Skarstein (SS), Sølvi Helseth (SH) and Lisbeth Gravdal Kvarme (LGK) declare that they have no competing interests.