RecruitingDiagnostic testTumor-Lymph Node MappingThe purpose of this study is to assess the feasibility and safety of ICG-guided intraoperative lymphography for detecting sentinel lymph nodes (SLN) in pediatric patients with solid tumors who require retroperitoneal lymph node dissection/sampling. This trial is a single-site cross-sectional study. The injection of ICG directly into lymphatics draining the primary tumor will take place at the time of operation after the patient is under anesthesia.