This specialist paper sets the basic hypothesis that the principle of the best interests of the child is a crucial component of standardization in the area of unlawful removal or retention of a child across the border - the so-called parental abduction of children. The hypothesis is confirmed through a review of normative acts at international, European and national levels. The auxiliary hypothesis focuses on the relationship between the two categories of protected fundamental human rights. In particular, it is questioned how the principle of the best interest of the child from Article 3 of the Convention on the Rights of the Child and the right to family life guaranteed by Article 8 of the European Convention on Human Rights. The auxiliary hypothesis is tested through relevant case law. The paper proves, i.e. disproves the consistency of the implementation of the protection of fundamental human rights in the proceedings of unlawful removal or retention of a child across the border. The topic of the paper is related to the legal protection of the child in cases of unlawful removal or retention across the border by one of the parents. Special emphasis is placed on the notion of the best interest of the child as a fundamental starting point in the creation of world, European and national policies for the protection and promotion of the rights of children, and also in the context of child abduction. The paper provides an overview of the most important legal documents related to the protection of the rights of the child, with reference to the proceedings for the return of a child who has been unlawfully removed or retained. Relevant cases from the case-law of the European Court of Human Rights, the Court of Justice of the European Union and the Constitutional Court of the Republic of Croatia are presented in this paper.