What is the most likely diagnosis for a child presenting with hematochezia, pain with defecation, and constipation?

The presentation of hematochezia, pain with defecation, and constipation in a child suggests an anal fissure as the most likely diagnosis.

An anal fissure is a tear in the lining of the anal canal, which often occurs in young children due to passing hard stools. The fissure causes sharp pain during bowel movements, which can lead to avoidance of defecation, resulting in constipation. The avoidance of bowel movements can worsen the situation since harder stools will continue to lead to more pain and subsequent bleeding, manifesting as hematochezia.

The symptoms are often more pronounced in children, as they may not be able to express discomfort effectively, leading to a cycle of pain and reluctance to pass stool. The characteristic bleeding from an anal fissure is usually bright red and occurs during or immediately after defecation, aligning well with the child's symptoms.

In contrast, other options would present differently; for instance, appendicitis typically involves pain in the right lower quadrant and fever, while hemorrhoids usually present with less severe pain and are often related to issues in older children or adults. Inflammatory bowel disease can include similar symptoms but usually presents with additional systemic signs such as weight loss or growth delays, and often involves chronic symptoms