**Core Concept**
The Mapleson breathing systems are a series of closed or semi-closed breathing circuits used in anesthesia to deliver a controlled mixture of gases to patients. Each circuit has its own set of characteristics, advantages, and limitations, which determine their suitability for specific patient populations.

**Why the Correct Answer is Right**
Mapleson circuits are classified into five types (A to E) based on their design and functionality. The Mapleson D circuit, also known as the Ayre's T-piece, is a simple, lightweight, and inexpensive circuit that is well-suited for pediatric anesthesia. This circuit consists of a simple tube with a Y-piece for the patient and a valve for the fresh gas flow. The Mapleson D circuit is ideal for children due to its low resistance to gas flow, which minimizes dead space and resistance to breathing.

**Why Each Wrong Option is Incorrect**
**Option A:** The Mapleson A circuit, also known as the Magill circuit, is commonly used in adult anesthesia due to its ability to handle high fresh gas flows and its resistance to rebreathing of carbon dioxide.

**Option B:** The Mapleson B circuit is not commonly used in pediatric anesthesia, as it requires a more complex design to minimize rebreathing of carbon dioxide.

**Option C:** The Mapleson E circuit, also known as the Jackson-Rees modification of the T-piece, is similar to the Mapleson D circuit but has a reservoir bag to store anesthetic gases. While it can be used in children, the Mapleson D circuit is more commonly used due to its simplicity and lower dead space.

**Clinical Pearl / High-Yield Fact**
The Mapleson D circuit is a popular choice for pediatric anesthesia due to its simplicity, low resistance to gas flow, and minimal dead space, making it ideal for children who require controlled ventilation.

**Correct Answer:** C. Mapleson D circuit (Ayre's T-piece)