Supplemental materials and data for: Lazić, A., Purić, D., & Krstić, K. (2021). Does parochial cooperation exist in childhood and adolescence? A meta-analysis. *International Journal of Psychology*, *56*(6), 917–933. https://doi.org/10.1002/ijop.12791. A free-to-read peer-reviewed version of the article is available at https://psyarxiv.com/uexmr/.