In a situation when a family does not care about the child and does not fulfil its educational duties to its child, and even where the support given does not result in an improvement of the situation, then the child may be placed in foster care. This leads to the child’s coexistence in two families: the biological one and foster one. In accordance with the law in force in Poland on family support and the foster care system of 20 September 2012, foster care becomes a supplement to parental care-giving and does not replace it. This article is an attempt to show the complexity of the issues concerning the upbringing of a child in two families. Particular attention is paid to the difficult situation of the child, who periodically, by the court’s decision is sent to foster care and functions in a new unrelated family, while maintaining contact with their biological parents, with whom they share a legal bond. This situation raises a number of difficulties experienced by the child – dilemmas and problems with identification and belonging to the foster or biological family. The temporary nature of foster care, its subsidiary character, causes that nowadays the goal of foster families is not to establish ties with the child similar to those resulting from a parent-like attitude but to support, help in the care and upbringing of the child. The article also highlights the resulting threats to the proper functioning of the child.