Over the past 30 years, the European Court of Human Rights (ECtHR) has increasingly applied the best interests of the child (BIC) principle in cases involving children. However, in the absence of a literal reference to the principle in the European Convention on Human Rights (ECHR), the principle’s inherent flexibility paves the way for contestable applications that result in the protection of adults rather than children. This is particularly true in the area of family law, where the interests of the child and those of the parents are closely intertwined. Given these structural and ontological limitations, one should ask to what extent the ECtHR is consistent with a reasonable application of the principle. This article aims to analyse the ECtHR’s application of the BIC principle in the specific area of family law disputes concerning the recognition of parenthood established through adoption and surrogacy. In such cases, the Court faces the challenge of striking a balance in the triangular relationship between the interests of the child, the parents and the State, while operating in an area significantly influenced by the margin-of-appreciation doctrine.