Shortly after the migration of the Ukrainian population had begun, a serious and urgent problem became apparent: there was a significant number of children arriving either unaccompanied or belonging to a care system unknown to Polish law. The exact number of unaccompanied minors who arrived in Polish territory from Ukraine has not been determined. On the basis of the collected data, it is possible to speak with high probability about tens of thousands and even more than 100,000 unattended children (Tymińska, 2022). The Polish Special Act introduced—with retroactive effect from 22 February 2022—an institution hitherto unknown to Polish law, i.e. temporary custody. This institution was supposed to regulate the relationship between the children and their de facto guardians, who would thus also assume primary responsibility for the child. Pursuant to Article 25 of the Special Act, a temporary guardian shall be appointed for a child whose stay has been legalised in connection with crossing the border after 24 February 2022 and who remains on the territory of the Republic of Poland unaccompanied by an adult authorised to represent the child and take care of the child’s property. The family court shall appoint a temporary guardian, taking into account the child’s best interests, primarily from among relatives, or other persons guaranteeing the proper performance of the guardian’s duties. If there are no such persons, the child must be placed with a foster family, a family orphanage or in institutional foster care, and a candidate for a temporary guardian is appointed within 48 hours by the social assistance centre. The same person may be the guardian of several children (especially siblings), provided there is no conflict between the interests of the minors. If a child in Ukraine was in a foster family or a family orphanage and has come with a guardian, the court will appoint that person as a temporary guardian. The law also provides temporary custodians and children in their custody with the right to free legal aid.