Dental caries remains a significant global health challenge, particularly among children. Silver diamine fluoride (SDF) has emerged as a minimally invasive, cost-effective intervention for arresting caries in primary teeth. This randomized controlled trial aimed to evaluate the effectiveness of SDF in arresting caries progression compared to fluoride varnish in young children. A total of 200 children aged 3–6 years with active caries lesions were randomly allocated into two groups: SDF (38%) and fluoride varnish (5%). Lesion activity was assessed at baseline, three, and six months using standardized criteria. The results demonstrated a significantly higher caries arrest rate in the SDF group (89.2%) compared to fluoride varnish (62.5%) (p<0.001). No significant adverse effects were reported aside from transient staining in the SDF group. These findings reinforce SDF’s superior efficacy in arresting caries progression, making it an effective strategy for children at high risk of untreated caries. Future studies should explore the long-term impact and parental acceptance of SDF in routine pediatric dental care.