Anal fissure: This is the most common cause of rectal bleeding in children, often due to constipation, diarrhea, or traumatic injury to the anal canal.

Constipation with rectal prolapse: Chronic constipation can lead to rectal prolapse, which may cause bleeding due to the prolapsed mucosa.
Gastroenteritis: Infections such as bacterial or viral gastroenteritis can cause rectal bleeding, especially if there is significant inflammation or ulceration in the rectum.
Inflammatory bowel disease (IBD): Conditions like Crohn's disease or ulcerative colitis can present with rectal bleeding, although they are less common in young children.
Food allergy or intolerance: Allergic reactions to certain foods, such as cow's milk, can cause rectal bleeding in infants and young children.

Intussusception: A condition where a part of the intestine telescopes into another, which can cause severe abdominal pain and rectal bleeding. It's a medical emergency that requires prompt diagnosis and treatment.
Meckel's diverticulum: A congenital anomaly of the small intestine that can cause rectal bleeding due to the presence of ectopic gastric mucosa.
Abuse or trauma: Physical abuse or accidental trauma can cause rectal bleeding, and it's essential to consider this possibility, especially in non-accidental injury cases.
Vascular malformations: Conditions like hemangiomas or arteriovenous malformations can cause rectal bleeding, although they are rare.

Juvenile polyps: Benign growths in the colon or rectum that can cause rectal bleeding, although they are relatively rare in children.
Colonic duplication: A rare congenital anomaly where a part of the colon is duplicated, which can cause rectal bleeding.
Hirschsprung's disease: A condition characterized by the absence of ganglion cells in the colon, leading to chronic constipation and potentially rectal bleeding.
Henoch-Schönlein purpura (HSP): A systemic vasculitis that can cause rectal bleeding, although it's more commonly associated with skin, joint, and kidney involvement.