In this paper, we have analyzed the legal norms that regulate the determination and challenge of maternity and paternity and the legal regulation of medically assisted fertilization. The aim of these mechanisms is to protect the rights of the child and his right to know his own origins. Determining the origin of the child creates a family law relationship between the parents and the child. In this regard, we analyzed all the mechanisms that exist in order for a child to exercise his right to know who his parents are. This results in the enjoyment of their care and other rights and obligations arising from the parent-child relationship. The presumption of maternity and the presumption of paternity, recognition of paternity, procedures for establishing and disputing maternity and paternity by a court decision are elaborated in detail. In all these proceedings, we must not neglect the role of the social welfare center, the court and other bodies involved in these processes. Croatian law regulates this matter in a manner consistent with the UN Convention on the Rights of the Child.