Background: Moral development (MD) arises from the interaction of attachment, temperament, emotion regulation, and decision-making. Children and adolescents with Attention-Deficit/Hyperactivity Disorder (ADHD) frequently show impairments across these domains, suggesting increased vulnerability to disruptions in MD. However, the mechanisms linking ADHD to MD remain poorly understood. Methods: A systematic review was conducted according to PRISMA 2020 guidelines. PubMed was searched for studies published between January 2014 and November 2024 examining MD-related constructs, including moral reasoning, fairness, aggression, bullying, callous–unemotional (CU) traits, decision-making, and reward sensitivity, in individuals aged 0–18 years with diagnosed or subclinical ADHD. Due to substantial heterogeneity in study design, measures, and outcomes, a qualitative synthesis was performed. Results: Of the 2104 records identified, 23 studies met inclusion criteria. Insecure or disorganized attachment, difficult temperament, and emotional dysregulation consistently emerged as developmental risk factors for impaired MD. Hyperactivity–impulsivity and deficient inhibitory control were strongly associated with aggressive and antisocial behaviors. Children with ADHD demonstrated a pronounced preference for immediate over delayed rewards, altered decision-making in social contexts, and reduced sensitivity to positive feedback. CU traits and aggression were frequently identified as behavioral correlates of MD impairments, particularly in interaction with family adversity and comorbid externalizing conditions. Social dysfunction, including bullying involvement, peer rejection, and interpersonal difficulties, was common and contributed to elevated long-term psychosocial risk. Conclusions: ADHD is associated with multidimensional vulnerabilities in MD through intertwined cognitive, emotional, and relational pathways. Interventions targeting attachment security, emotion regulation, reward processing, and social skills may foster MD and reduce later social difficulties. Longitudinal and cross-cultural research is needed to clarify causal mechanisms and inform developmentally sensitive prevention and treatment strategies.