Purpose: Vitamin B12 deficiency is a cause of preventable growth and developmental retardation in children. In this respect, alternative methods such as oral and sublingual treatments are being tried. We aimed to compare the efficacy of oral, sublingual, and intramuscular vitamin B12 treatments in children aged 0-3 years. Methods: The study included 158 patients with serum vitamin B12 deficiency (serum vitamin B12 level <300 ng/L) aged 0-3 years retrospectively. According to the vitamin B12 treatment modalities, the patients were divided into three groups as oral cyanocobalamin (group 1), sublingual methylcobalamin (group 2), and intramuscular cyanocobalamin (group 3). Results: The mean values of vitamin B12 levels increased to above 300 ng/L in all three groups. This increase was statistically significant for Group 1,2 and 3 (p<0.05). Conclusion: Sublingual methylcobalamin was determined as effective as oral and intramuscular cyanocobalamin improving vitamin B12 levels aged 0-3 years. What's already known about this topic? It is already known that intramuscular and oral cyanocobalamin treatments are effective in vitamin B12 deficiency of children. What does this article add? Sublingual methylcobalamin treatment, which is a new treatment method, was found to be as effective as oral and intramuscular cyanocobalamin treatments. To our knowledge, there is no study about sublingual treatment in children and comparing oral cyanocobalamin, intramuscular cyanocobalamin, sublingual methylcobalamin.