ABSTRACTStability is vital for the development, health and relationships of children in family foster care. Instability can lead to social and school issues, low self‐esteem and diminished trust in caregivers. This article examines the risk and protective factors for stability for these children. Data, drawn from case files in six municipalities (n = 116), combine qualitative and quantitative analyses for a comprehensive understanding. Twenty children from each municipality were selected, with 10 in stable placements (lived in one family foster home for over a year) and 10 in unstable placements (lived in at least two different family foster homes). Quantitative results highlight the importance of factors like familiar placements, a child's age at the time of placement, behavioural challenges and the number of children in the foster home. Stable placements were more common in homes with fewer children (including foster and biological children). Qualitative findings show that in some instances, breakdowns in foster care placements could not be foreseen, often arising from stressful events within the foster family's life after the child's placement. Additionally, we observed that breakdowns sometimes resulted from foster parents lacking the necessary resources to address the child's requirements, particularly in cases involving children with behavioural challenges or extensive needs.