Received: 6 March 2020
Accepted: 24 September 2020
First Online: 29 September 2020
Ethics approval and consent to participate
: We provided parents with information on the purpose and procedure of the study and collected written informed consent from them before enrollment. This study was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. The study protocol was approved by the Institutional Review Board of the Korean Institute of Child Care of Education (KICCEIRB-2016-07).
: Not applicable.
: The authors declare that they have no competing interests.