Article History
Received: 26 April 2018
Accepted: 5 June 2018
First Online: 14 June 2018
Ethics approval and consent to participate
: All parents have given their written informed consent to participate in the study. The study protocol was approved by Regional Ethics Committee (2012/63/REK nord) and meets the standards of the Declaration of Helsinki.
: The authors declare that they have no competing interests.
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