**Core Concept**
Perthes disease, also known as Legg-Calve-Perthes disease, is a childhood hip disorder characterized by the temporary loss of blood supply to the femoral head, leading to its necrosis and deformation. This condition typically affects children between 4 to 7 years of age.

**Why the Correct Answer is Right**
Perthes disease is a common cause of hip pain and limp in children, especially in the age group of 4 to 7 years. The condition is often bilateral and can lead to femoral head deformity and arthritis in later life if left untreated. The exact cause of Perthes disease is unknown, but it is believed to be related to a temporary interruption in the blood supply to the femoral head, leading to ischemia and necrosis of the bone tissue.

**Why Each Wrong Option is Incorrect**
**Option A:** Septic arthritis is a condition where the joint space becomes infected with bacteria, leading to inflammation and pain. While septic arthritis can cause a limp in a child, it is typically associated with a high fever, joint swelling, and systemic symptoms, which are not mentioned in the question.

**Option B:** Slipped capital femoral epiphysis (SCFE) is a condition where the growth plate in the femoral neck is disrupted, causing the femoral head to slip out of place. SCFE typically affects adolescents, especially those with obesity or other underlying conditions, and is not as common in children as young as 3 years old.

**Option D:** Developmental dysplasia of the hip (DDH) is a condition where the hip joint is not properly formed, leading to instability and potential deformity. While DDH is a common cause of hip problems in children, it typically presents at birth or in early infancy, not at the age of 3.

**Clinical Pearl / High-Yield Fact**
Perthes disease is often associated with a delay in diagnosis, as the symptoms may be nonspecific and can be mistaken for other conditions. It is essential to consider Perthes disease in the differential diagnosis of a child presenting with a limp, especially if they are between 4 to 7 years old.

**Correct Answer:** C. Perthe's disease