The project consists of two parts: A longitudinal developmental outcome study for children in foster families (GROW-part) and an intervention study (TREAT-part), which is embedded in the longitudinal study. We intended to recruit a total of 250 children aged between two and seven years. Of these, 100 foster children with previous experiences of maltreatment (including experiences of physical, sexual, emotional or psychological abuse and/or neglect) were planned to be included in the TREAT-part and randomly assigned to either usual care or a foster parent-based intervention to increase resilience in foster children. Moreover, 150 children living with their biological parents and without experiences of maltreatment were planned to be recruited as a developmental comparison group (GROW-part). The final sample size includes 94 foster children and 157 biological children.

The goal of the GROW-part is to compare the development of children with maltreatment experiences in foster families with the development of children without maltreatment experiences living in their original family across three measurement time points at six-monthly intervals. The primary developmental outcome addressed in the longitudinal study is related to indicators of child mental health, specifically emotional and behavioral problems, and future incidences of maltreatment.

The goal of the TREAT-part is to investigate the specific and additional impact of a parent-focused intervention to support foster parents in raising maltreated children. The TREAT-part includes supporting foster parents in learning to help children in building self-esteem, managing child misbehavior appropriately and raising resilient children. The primary outcome is related to the foster parent-child relationship and changes in placements. Secondary outcomes are child conduct and anxiety problems.

Both parts (GROW&TREAT) will be completed by a subproject specifically focusing on neurobiological (HPA-functioning, sleep, immunological parameters) and neurocognitive alterations (emotion recognition, emotion regulation and cognitive control) associated with early maltreatment experiences. These alterations will be investigated before and after the intervention in all children in order to delineate not only the association between neurobiological changes in the stress response system and emotional/behavioral dysregulation, but also to evaluate neurobiological effects of the intervention.