**Core Concept**
The first session with a child patient is a crucial step in building trust and establishing a therapeutic relationship. It involves gathering information about the child's medical, social, and emotional history, as well as the presenting problem or complaint. The primary aim of this initial session is to establish a rapport with the child and their caregivers, while also gathering essential information to inform further assessment and treatment.

**Why the Correct Answer is Right**
The first session is essential for establishing a therapeutic alliance, which is critical for the success of any treatment plan. This involves creating a safe and supportive environment where the child feels comfortable sharing their concerns and feelings. The clinician should also use this opportunity to gather information about the child's medical history, including any previous illnesses, allergies, and medications. Additionally, the clinician should inquire about the child's social and emotional history, including their family dynamics, relationships with caregivers, and any previous experiences with healthcare providers.

**Why Each Wrong Option is Incorrect**
**Option A:** Gathering information about the child's medical, social, and emotional history is a key aspect of the first session, but it is not the only aim. While it is essential to establish a rapport with the child and their caregivers, this is not the primary focus of the first session.
**Option B:** Assessing the child's physical health is an important aspect of the first session, but it is not the primary aim. While a physical examination may be performed, the focus of the first session is on gathering information and establishing a therapeutic relationship.
**Option C:** Developing a treatment plan is not typically the focus of the first session. While the clinician may begin to formulate a plan, the primary aim of the first session is to gather information and establish a therapeutic relationship.

**Clinical Pearl / High-Yield Fact**
A good first session should leave the child and their caregivers feeling heard, validated, and understood. It is essential to strike a balance between gathering information and providing emotional support, as this will help establish a strong therapeutic alliance and set the stage for successful treatment.

**Correct Answer: D. Developing a treatment plan.**