Colorectal carcinomas occur primarily in elderly people and are rare in children. Unlike adult colorectal carcinomas, the overall prognosis is very poor because of the usual delay in diagnosis and advanced stages at presentation or initial diagnosis, and a high incidence of aggressive tumor pathology such as mucinous adenocarcinoma. Colon cancer should not be excluded in children only based on age or barium enema results. Therefore, colonoscopy should be performed in pediatric patients with unexplained rectal bleeding and abdominal pain. We report a rare case of a child with a mucinous adenocarcinoma of the sigmoid colon in a 12-year-old boy, who presented with an abdominal mass and abdominal pain and review the medical literature.