Background: The full scope of coronavirus disease 2019 (COVID-19) remains unknown, and a definitive treatment for children has yet to be established. N-acetylcysteine (NAC), beyond its mucolytic effect in lung disorders, operates through various mechanisms, such as enhancing the immune system, inhibiting viral replication, and reducing inflammation. These pharmacological properties of NAC suggest it is a potential therapeutic agent for COVID-19. Objectives: Our goal was to evaluate whether NAC could improve outcomes in hospitalized children presenting with acute respiratory symptoms due to COVID-19. Methods: Fifty-eight patients with moderate COVID-19 symptoms were randomly allocated to receive either 1200 mg/day of NAC or a placebo for 7 days. We monitored NAC-related side effects, C-reactive protein (CRP) levels, white blood cell (WBC) count, serum creatinine, oxygen saturation, hospital stay duration, and clinical symptoms. Results: All measured variables in both groups showed significant improvement by the end of the study. However, the analysis indicated that the changes in CRP and WBC levels in the NAC group, compared to the placebo, were not significant (P = 0.659 and 0.067, respectively). There was a notable improvement in oxygen saturation in the NAC group versus the placebo group at the study's conclusion (P = 0.001). The length of hospital stay and CRP levels significantly decreased in the NAC group compared to the placebo group (P-value = 0.001 and P-value ≤ 0.001, respectively). Additionally, the mortality rate was 0.0% in the intervention group versus 7.4% in the placebo group (P-value = 0.491). Conclusions: The findings from this study support the potential of NAC in shortening hospital stay durations and enhancing oxygen saturation among children with COVID-19.