Background Onychomycosis was an ignored disease in children, and the prevalence was still unknown worldwide. Objectives This study was conducted to investigate the prevalence and treatment regimens of onychomycosis in children younger than 18 years old. Methods We systemically reviewed all publications by searching the key terms to reveal the onychomycosis in children from 1990 to 2022. Results A total of 44 articles including 2,382 children with onychomycosis were enrolled in this study. The male to female ratio was 1.29:1. The youngest child was 35 days old and the average age was 9.8 years old. The duration of disease usually ranged from 7 days to 4 years. Onychomycosis in children was more prevalent in toenails compared to fingernails (77.6% vs. 18.4%), and 4% patients had both. A total of 527 children (22.12%) had concomitant tinea pedis infection, and in 267 patients (11.21%), their family members had onychomycosis or tinea pedis. The most common clinical type of onychomycosis was DLSO (67.74%) and the predominant isolates were T. rubrum (66.13%), followed by C. albicans (9.08%) and T. mentagrophytes complex (5.34%). There were 419 children (74.03%) receiving systematic treatment only, 74 patients (13.07%) receiving topical treatment only, and 73 patients (12.90%) receiving both systematic and topical treatment. Twelve patients (2.12%) had mild drug‐related side effects. During the follow‐up, 71.25% children were cured, 17.50% symptoms improved and 4.17% failed. Conclusions Onychomycosis was underestimated in children and the diagnosis of onychomycosis should be properly considered in children with nail disorders. For mild patients, topical treatment can be a good choice, and oral antifungal drugs could be added to severe individuals under monitoring.