During infancy and early childhood, obtaining the adequate amount of appropriate nutrition has paramount importance for the full development of a child’s potential. The focus of this study was to evaluate the complementary food produced by solid-state fermentation of fonio and soybean using Rhizopusoligosporus (2710) and orange-fleshed sweet potatoes (OFSP) using Lactobacillus planterum (B-41621). Solid-state fermentation (SSF) was carried out by inoculating fonio and soybean with a spore suspension (1 × 10⁶ spores/mL) of Rhizopusoligosporus (2710) and OFSP with a spore suspension (1 × 10⁶ spores/mL) of Lactobacillus plantarium (B-41621). The samples were blended in the following ratios: fonio and soybean 100: 100 (AS), fonio/soybean and OFSP 50: 50(ASO). These were compared with a commercial infant formula, which served as the control (CTRL). Quality characteristics of the samples were evaluated. The results showed that moisture, crude protein, fiber, ash content, beta carotene, iron and titratable acidity ranged from 54.97–56.27, 17.10–19.02%, 7.08–7.60%, 2.09–2.38%, 15.80–17.35 mg/100 g, 6.57–8.41 mg/100 g and 0.16–0.48%, respectively. An increase in fermentation time significantly (p < 0.05) increased these contents. In sensory scores, there were no significant (p > 0.05) differences between the average mean scores of the samples. This study shows that nutrient-rich complementary food of acceptable quality can be produced from blends using SSF for the optimum growth and development of infants.