Most common abdominal mass in children:

c. Neuroblastoma(Ref: Nelson's 20/e p 2464-2466, Ghai 8/e 617-618)Neuroblastoma is the most common extracranial solid tumor in childrenLocalized Neuroblastoma can manifest as an asymptomatic mass or can cause symptoms because of the mass itself, including spinal cord compression, bowel obstruction & superior vena cava syndrome.Note: Both Neuroblastoma & Wilms' tumor can present as abdominal mass in children but Neuroblastoma is more common than Wilms' tumor, so it is the better answer to this question