Trevlas Ε., and Tsigilis Ν. “Evaluation of the Influence of a Physical Education Program on Playfulness of Preschool Children: A Qualitative Approach”. Inquiries in Physical Education and Sport, vol. 6, no. 1, July 2008, pp. 1-13, doi:10.26253/heal.uth.ojs.ispe.2008.1226.