Vorkapić, S. T., and A. Babić Šikić. “What Pre-School Children Think about Happiness, Hope, Gratitude, Wisdom, Justice, and Optimism? The Positive Conceptual Thinking Development Study”. Journal of Positive School Psychology , vol. 3, no. 1, July 2018, pp. 1-25, https://journalppw.com/index.php/JPPW/article/view/59.