**Core Concept**
Rectal bleeding in a toddler can be caused by various conditions, including anal fissures, rectal polyps, or intussusception. However, the most probable diagnosis among the given options is intussusception, a condition where a part of the intestine invaginates into another, leading to obstruction and ischemia.

**Why the Correct Answer is Right**
Intussusception typically occurs in children between 6 months to 3 years of age and is often caused by a lead point, such as a Meckel's diverticulum, lymphoid hyperplasia, or a rectal polyp. The presentation of intussusception is often characterized by sudden onset of abdominal pain, vomiting, and rectal bleeding. The bleeding can range from occult to gross, and the frequency of the bleeding can vary. In some cases, the bleeding may be the only symptom, making it essential to consider intussusception in the differential diagnosis of rectal bleeding in toddlers.

**Why Each Wrong Option is Incorrect**
**Option A:** Anal fissure is a possible cause of rectal bleeding in toddlers but is less likely to present with the sudden onset of symptoms and more likely to be associated with painful defecation.
**Option B:** Rectal polyp is a possible cause of rectal bleeding but is less common in toddlers and more likely to be associated with other symptoms such as constipation or abdominal pain.
**Option C:** Rectal foreign body is a possible cause of rectal bleeding in toddlers but is less likely to present with the sudden onset of symptoms and more likely to be associated with a history of inserting objects into the rectum.

**Clinical Pearl / High-Yield Fact**
Intussusception can be diagnosed using a combination of clinical presentation, imaging studies (e.g., ultrasound, X-ray), and sometimes, air enema. It is essential to consider intussusception in the differential diagnosis of rectal bleeding in toddlers and to have a high index of suspicion for this condition.

**Correct Answer:** C. **Intussusception**