Background: Parent-supported psychosocial development programs aim to strengthen the parent-child relationship and promote healthy early childhood development, particularly in settings where access to structured preventive interventions is limited. Aims To evaluate the effectiveness of a structured parent-supported psychosocial development program on psychosocial outcomes in children aged 1-3 years and to examine its secondary effects on parental anxiety.Methods A waiting-list randomized controlled trial with pretest, posttest, and follow-up assessments was conducted online in Türkiye between November 2024 and February 2025. Forty-three parents of children aged 1-3 years were randomly assigned to the intervention (n=22) or control group (n=21). The six-week structured program consisted of six modules covering 11 topics. Parents in the intervention group received weekly PDF-based educational materials and participated in online group discussions. Results: Psychosocial development scores at posttest and follow-up were significantly higher in the intervention group compared with the control group (p<0.05), with significant group and group*time interaction effects. No significant differences were found between groups in parental anxiety levels (p>0.05). Conclusions: The parent-supported program was effective in improving psychosocial outcomes among children aged 1-3 years but did not reduce parental anxiety. Future interventions should consider incorporating strategies specifically addressing parental anxiety to enhance the effectiveness of early psychosocial support programs. Trial registration: ClinicalTrials.gov Identifier: NCT06951165