Introduction: Breastfeeding is widely recognised as a key determinant of child health and development, with growing evidence suggesting a beneficial role in early cognitive and neurodevelopmental outcomes. However, evidence synthesis focusing specifically on children aged 2 to 3 years remains limited, despite this being a critical period of brain maturation and functional development. Objective: This rapid review aimed to synthesise recent evidence on the association between breastfeeding practices—including duration and exclusivity—and cognitive and neurodevelopmental outcomes in children aged 2 to 3 years. Methods: A rapid literature review was conducted in accordance with the WHO Rapid Review Guide and reported following PRISMA guidelines. A systematic search of PubMed, CINAHL, and Web of Science was performed for studies published between January 2021 and December 2025. Eligible studies included observational designs assessing breastfeeding exposure and cognitive or neurodevelopmental outcomes in children aged 24–36 months. Study selection, data extraction, and methodological quality appraisal were conducted by independent reviewers. Findings were synthesised narratively using a thematic approach. Results: Six studies met the inclusion criteria, comprising four longitudinal cohort studies and two large-scale cross-sectional analyses conducted across diverse geographical settings. Overall, longer breastfeeding duration was consistently associated with more favourable neurodevelopmental outcomes, including higher global developmental scores, improved language and socioemotional development, and markers of advanced brain microstructural maturation. Evidence of a dose–response relationship was observed, with breastfeeding for 7–12 months showing the most robust associations across multiple developmental domains. Exclusive breastfeeding for six months was particularly associated with improved communication and problem-solving skills in low-resource settings. While exclusive breastfeeding was not consistently associated with long-term cognitive trajectories, cumulative breastfeeding exposure was linked to higher baseline cognitive performance in early childhood. Conclusions: This rapid review suggests that breastfeeding, particularly when sustained beyond the early postnatal period, is positively associated with cognitive, neurobiological, and socioemotional development in children aged 2 to 3 years. Although causal inference is limited by the observational nature of the evidence, the overall consistency and biological plausibility of findings support current public health recommendations promoting exclusive and continued breastfeeding as part of strategies to optimise early childhood development.