Diagnostic invalidation—the dismissal, minimization, or delegitimization of a patient’s reported symptoms or illness experience—may be an underrecognized source of pediatric medical trauma. Existing pediatric medical traumatic stress frameworks emphasize acute illness, invasive procedures, intensive care, and other visibly threatening events. This narrative review integrates literature on pediatric medical traumatic stress, symptom invalidation, diagnostic overshadowing, epistemic injustice, functional and chronic symptoms, patient–clinician trust, and trauma-informed care. It proposes that repeated invalidation may contribute to traumatic stress through prolonged suffering, loss of bodily and epistemic agency, relational betrayal, stigmatization, unpredictability, and dependence on healthcare systems perceived as unsafe. Downstream effects may include altered symptom disclosure, delayed or avoidant care-seeking, hypervigilance, distrust, fragmented care, and reluctance to engage in appropriate psychological treatment. The review distinguishes validation from premature diagnostic agreement and presents a six-part clinical framework—Hear, Acknowledge, Explain, Respond, Reassess, and Partner—for maintaining diagnostic rigor while preserving relational safety. A conceptual model describes a recursive pathway through which invalidation-related stress responses may contribute to increasingly difficult clinical encounters and further skepticism. Because direct longitudinal pediatric evidence remains limited, the model is hypothesis-generating. Recognizing diagnostic invalidation as a relational and patient-safety concern may broaden trauma-informed pediatric practice beyond procedural distress.