A nurse is preparing to administer a vaccine into the deltoid muscle of a preschooler. Which of the following actions should the nurse take?

The correct answer is D: Use a 1.8 mm (0.5 in) needle. For a preschooler, a shorter needle is recommended to avoid reaching deeper tissues or causing unnecessary pain. Using a 1.8 mm needle ensures the vaccine is injected into the deltoid muscle without penetrating too deeply. Choices A, B, and C are incorrect. A 15┬░ angle is not necessary for a deltoid muscle injection, inserting below the acromion process may not target the deltoid muscle accurately, and a 20-gauge needle may be too thick for a preschooler.