The paper begins by exploring assumptions regarding the vulnerability of children who participate in South Australia's (SA's) criminal justice system. The most fundamental assumption of the past 10 years has been that some victims/witnesses are more vulnerable than others, an assumption that has been acted on in legislative changes designed to accommodate such vulnerable child witnesses. Under SA legislation, vulnerable witnesses are defined as those under 16 years old, those who have an intellectual disability, alleged victims of a sexual offense to which the proceedings relate, or those having some special disadvantage related to the circumstances of the case or the witness. Under the legislation, those witnesses deemed to be "vulnerable" are given the opportunity to testify under conditions that will protect the witness from embarrassment or distress and the intimidation of the courtroom atmosphere. The assumption that young children are inherently vulnerable to harm by traditional criminal justice witness management is challenged by the authors of this paper, based on their experience. They advise that younger children in many cases have more family support, can be more often believed by adults at the time of disclosure, and can have greater access to formal support than some older children. Young children are also often given less intense and intimidating cross-examination by defense counsel. Older children, on the other hand, are at risk of experiencing various disadvantages and risk of harm due to their being perceived as more sexually aware than younger children and more likely to have a motive to make an accusation of sexual abuse and to understand the consequences of such an allegation for an accused person. The writers raise this issue in order to prevent generalized vulnerability assumptions based on a child's age and to argue for a more precise framework for vulnerability assessments on a case-by-case basis. The proposed psycho-social model of vulnerability assessment assesses the following three components separately and in their interaction: the person, his/her environment, and his/her position in the criminal justice system. It is important to examine the internal pressure on the individual, the external pressure on the individual, and current life situations that may impact on the individual's ability to intervene effectively on all levels. Another underlying assumption with this model is that change in one part of the system affects the whole system and the subsequent interactions. In viewing this model in conjunction with the complexities of the criminal justice system, there is a need to monitor the individual, his/her environment, and the features of the criminal justice system. In order to make appropriate assessments within both the practice reality and theoretical framework, this paper proposes an assessment tool that can be used when prioritizing caseloads, allocating resources, and in appropriately directing case planning and support. The authors provide a detailed outline of the tool's assessment of individual factors, environmental factors, and criminal justice system factors. 13 notes