Funding for this research was provided by:
Universitetet i Agder
Received: 29 June 2018
Accepted: 29 April 2019
First Online: 14 May 2019
Ethics approval and consent to participate
: This trial was approved by the Norwegian Centre for Research Data, 29/06/2017, ref.: 48643. Written consent was obtained from all parents when they chose to sign up for participation.
: Not applicable
: The authors declare that they have no competing interests.
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