Purpose To assess the efficacy of primary sternal closure technique compared to vacuum-assisted closure technique in treatment of post-cardiac surgery mediastinitis in paediatric age group. Additionally, assessed postoperative need for IV drug use, hospital stay length, wound and sternal healing and survival. Hypotheses: primary sternal closure is a reliable technique for treatment of poststernotomy mediastinitis following cardiac surgery in paediatric age group. Materials and Methods A prospective randomized controlled trial included 217 pediatric patients developed post-cardiac surgery mediastinitis from 2016 to 2022. They were randomly divided into primary sternal closure group (A) and vacuum-assisted closure group (B) and operated by two cardiothoracic surgeons. Follow-up of the patients was done for 6-months duration following treatment of mediastinitis to assess postoperative need for hospitalization, IV drug use, wound complications, sternal stability and survival. Results The final analysis included 101 patients in each group. The chance of survival over 6 months after surgery was more for primary sternal closure group (175.2) days versus (157.6) days for the vacuum-assisted closure group, with significant difference Log Rank test p-value (0.005). Duration for IV antibiotics use in the primary closure group was 8.55±3.57 and it was 32.61±8.39 showing high statistically significant difference (p<0.001). Patients in the primary closure group had earlier discharge from hospital 15.77±4.18 than vacuum assisted group 42.61±8.39, with high statistically significant difference (p<0.001). Primary closure group showed better sternal stability and sternotomy wound healing on clinical follow-up. Conclusion Primary sternal closure technique is a favorable technique over vacuum-assisted closure technique for treatment of paediatric mediastinitis following cardiac surgery. The reinforced sternal closure technique is a reliable technique with promising results regarding IV drugs need, hospitalization duration, survival and sternotomy wound healing.