<p>Care-experienced children are known to have histories of adverse childhood experiences (ACEs). Exposure to adversity is a well known risk factor for negative outcomes across the lifespan. However, very little is known about the adversity histories of young children in care, and how this may affect their emotional, behavioural, and attachment disorder outcomes over time. Data from 378 young children in foster care, aged 0–5 years old, as part of the Best Services Trial (BeST^?) were used. Adversity experiences were identified and coded by reviewers from social care records. Age at entry to care was also recorded. Outcome variables used in this study included emotional and behavioural difficulties and attachment disorder symptoms measured at two timepoints (a few weeks after entering care, and 2.5 years later). The number of ACEs in this sample was high, with around two thirds of children having experienced 4 or more. The older the age at which a child entered foster care was strongly related to higher number of ACEs, and increased severity of maltreatment, experienced. An increase in emotional and behavioural difficulties after 2.5 years in care was significantly uniquely predicted by the number of pre-care ACEs a child experienced. Attachment disorder symptoms were significantly lower at 2.5 years in care as compared to levels at entry to care. These findings indicate that prevention and early identification of risk in vulnerable families is paramount. Additionally, tailored interventions for the emotional and behavioural wellbeing of young children in care is essential.</p>