Emotional instability and poor emotional awareness are cardinal features of the emotional dysregulation associated with borderline personality disorder (BPD). Most models of the development of BPD include child negative emotional reactivity and grossly inadequate caregiving (e.g., abuse, emotional invalidation) as major contributing factors. However, early childhood emotional reactivity and exposure to adverse family situations are associated with a diverse range of long-term outcomes. We examine the known effects of these risk factors on early childhood emotional functioning and their potential links to the emergence of chronic emotional instability and poor emotional awareness. This examination leads us to advocate new research directions. First, we advocate for enriching the developmental assessment of children's emotional functioning to more closely capture clinically relevant aspects. Second, we advocate for conceptualizing children's early family experiences in terms of the proximal emotional environment to which young children may be or become sensitive. Such approaches should contribute to our ability to identify risk for BPD and guide preventive intervention.