Final answer:
The nurse's priority action for a child with sickle cell anemia experiencing severe symptoms is to ensure adequate oxygenation and manage pain.
Step-by-step explanation:
The nurse's priority action for a child with sickle cell anemia experiencing severe chest pain, fever, a cough, and dyspnea would be to ensure adequate oxygenation and manage pain. The nurse should assess the child's oxygen saturation levels using a pulse oximeter and administer supplemental oxygen if necessary. Additionally, the nurse should provide pain relief medication to alleviate the chest pain.