Introduction: Childhood obesity is associated with an increased risk of vitamin D deficiency due to volumetric dilution, adipose sequestration, and altered metabolism. Vitamin D plays a crucial role in bone health, immune function, and metabolic regulation; however, optimal supplementation strategies for children with obesity remain unclear. Current paediatric guidelines do not provide specific recommendations for this population. This review evaluates the prevalence of vitamin D deficiency in children with obesity and summarises evidence on effective supplementation regimens. Methods: A structured narrative review of literature up to February 2026 was conducted using PubMed and Google Scholar. Clinical trials involving children with obesity aged 5–20 years, with clearly defined methodology and reported 25(OH)D concentrations, were included. Results: Children with obesity demonstrate a blunted response to vitamin D supplementation compared with normal-weight peers. Standard doses (400–2,000 IU/day) frequently fail to achieve serum 25(OH)D ≥30 ng/mL. Higher doses (≥4,000 IU/day or equivalent weekly/monthly regimens) are more effective in normalising vitamin D status. No significant adverse effects were reported across included studies. Conclusions: Children with obesity may require individualised, higher-dose vitamin D supplementation to achieve adequate serum 25(OH)D levels. Further research is needed to establish evidence-based dosing guidelines and to evaluate long-term safety in this population.