**Core Concept**
The ECG of a newborn child with Down syndrome may exhibit characteristic changes due to the association of Down syndrome with congenital heart defects, particularly atrioventricular septal defects. These defects can lead to alterations in cardiac conduction and repolarization.

**Why the Correct Answer is Right**
The most common ECG finding in newborns with Down syndrome is the presence of a prolonged PR interval, often exceeding 0.20 seconds. This is due to the increased likelihood of atrioventricular septal defects and abnormalities in the atrioventricular conduction system. Additionally, left ventricular hypertrophy and right axis deviation may also be observed.

**Why Each Wrong Option is Incorrect**

* **Option A:** This option is incorrect because it does not specify the characteristic ECG finding associated with Down syndrome in newborns.
* **Option B:** This option is incorrect because it does not mention the prolonged PR interval, which is a hallmark ECG finding in newborns with Down syndrome.
* **Option C:** This option is incorrect because it does not accurately describe the ECG changes associated with Down syndrome in newborns.
* **Option D:** This option is incorrect because it does not provide a specific ECG finding that is characteristic of Down syndrome in newborns.

**Clinical Pearl / High-Yield Fact**
Newborns with Down syndrome are at increased risk of congenital heart defects, particularly atrioventricular septal defects. The presence of a prolonged PR interval on ECG should prompt further evaluation for cardiac anomalies.

**Correct Answer:** B. Prolonged PR interval