## **Core Concept**
Hematochezia refers to the passage of fresh blood through the anus, often originating from the lower gastrointestinal tract. In children, the causes of hematochezia can vary based on age and other factors. Understanding the common causes helps in diagnosing and managing the condition effectively.

## **Why the Correct Answer is Right**
The most common cause of hematochezia in children is **anal fissures**. Anal fissures are small tears in the skin around the anus, which can cause pain and bleeding during and after bowel movements. This condition is prevalent in children due to factors like constipation, which leads to hard stools that can tear the anal skin.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While rectal polyps can cause hematochezia, they are less common in children compared to anal fissures.
- **Option B:** Infectious colitis can cause hematochezia, but it is typically accompanied by other symptoms like diarrhea, fever, and abdominal pain, making it less likely to be the most common cause.
- **Option C:** This option is not provided, but based on common causes, conditions like intussusception or Meckel's diverticulum are more severe and less common than anal fissures.
- **Option D:** While other conditions like inflammatory bowel disease can cause hematochezia, they are less common in children compared to anal fissures.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that in children, **anal fissures** are often associated with constipation and can be diagnosed by a simple physical examination. Treatment usually involves measures to soften stools and promote healing of the fissure.

## **Correct Answer:** B. Anal fissure.