Which intervention should the nurse implement first?

The correct answer is C: Explain the procedure to the toddler using simple language. This intervention should be implemented first to reduce the toddler's anxiety and fear, promote trust, and increase cooperation during the injection. By providing a clear explanation in simple language, the nurse can help the toddler understand what will happen, which can help alleviate stress. Gathering supplies (B) and assessing vital signs (D) are important but should come after establishing communication with the toddler. Restraint (A) should be avoided as it can escalate fear and may not be necessary with effective communication.