Article History
Received: 24 July 2016
Accepted: 27 March 2018
First Online: 3 April 2018
Authors’ information
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: The written informed consent to this research study was obtained from parents. The paper has been approved by Medical University of Lublin Bioethical Committee (number KE-0254/74/2009).
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: The authors declare that they have no competing interests.
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