A proper preparation for foster parents to care for abused and neglected children includes effective training and initial diagnostics in order to plan individual treatment. Hence, a basic knowledge about the main psychosocial and developmental problems associated with abuse and neglect and their prevalence in foster children is needed. For this purpose, a systematical literature review and a series of meta-analyses were conducted. A total of 25 studies reporting data on development (n = 4,033), mental health (n = 726), and attachment (n = 255) of foster children in preschool age met the inclusion criteria. The meta-analyses indicated prevalence rates of approximately 40% for developmental, mental health problems, and insecure attachment. Rates of disorganized attachment were estimated to 22%. These findings outline the necessity of an initial trauma-oriented diagnostics and trainings for foster parents that address foster children’s development, mental health, and disorganized attachment.