Received: 5 March 2020
Accepted: 12 June 2020
First Online: 22 June 2020
Ethics approval and consent to participate
: This study was conducted anonymously including children ages 5–12. We obtained verbal and written informed consents from a parent or guardian on behalf of all participants at the parent-teacher conference, and then sent a questionnaire with a detailed informed consent to them. The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of Xi’an Jiaotong University (Project identification code:2016–0985).
: Not applicable.
: The authors have no competing interests to declare.