Funding for this research was provided by:
Christian-Albrechts-Universität zu Kiel (F356910)
Received: 22 June 2019
Accepted: 12 September 2019
First Online: 25 October 2019
Ethics approval and consent to participate
: The study was approved by the Institutional Ethics Committee (EK 119/08 and 154/11). The authors complied with the World Medical Association Declaration of Helsinki regarding ethical conduct of research involving human subjects. Written informed consent was obtained from all participating parents.
: Not applicable.
: The authors declare that they have no competing interests.