Final answer:
The priority action by a nurse for a child in anaphylactic shock is to assess the child's airway and breathing, followed by administration of epinephrine.
Step-by-step explanation:
The priority action for a nurse caring for a school-age child experiencing an anaphylactic reaction is C) Assessing the airway and breathing. This is because ensuring the airway is not obstructed and that the child can breathe is critical in such a severe allergic response. Once the airway and breathing are secured, the next step would typically be the administration of epinephrine, as it is the first-line treatment for anaphylaxis. Epinephrine works to raise blood pressure, relax bronchial smooth muscle, modulate heart rate, and reduce swelling, mitigating the life-threatening consequences of anaphylactic shock. While informing the child's parents and administering an antihistamine are also important, these actions are secondary to immediately addressing the acute medical emergency presented by anaphylaxis.