Child abuse has negative health consequences. Early detection and preventive measures lead to avoidance of prolonged and more complex problems. School nurses have a child protection role and should pay attention to vulnerable children. Through health dialogues and other interactions with pupils, school nurses have the opportunity to detect child abuse. The aim of the study was to explore how school nurses detect child abuse and initiate support measures. Focus group interviews were conducted with 23 school nurses. The data were analyzed using a grounded theory approach. Results showed that the main concern of the school nurses was support and assistance to children who are abused which was preceded by a trust-creating and trust-strengthening process. Trust contains self-confidence and confidence in the system and trust can be strengthened or undermined. Building trustful relations is time consuming and is facilitated by networking, refined assessment instruments, and collaboration.