Final answer:
The priority nursing intervention is to protect the child from harm during the seizure, which involves ensuring a safe environment and placing the child in the recovery position to maintain a clear airway and prevent aspiration.
Step-by-step explanation:
The priority nursing intervention for a 4-year-old boy having a febrile seizure during a well-child visit is D) Protecting the child from harm during the seizure. During a seizure, ensuring the child does not hurt themselves is crucial. This includes moving nearby objects that could cause injury and placing the child in a safe position.
Despite Option A mentioning placement on the side and hyperextending the head, which is partially correct, it compromises the airway by hyperextending the head. Option B is incorrect, as holding the child still is not recommended because it can cause injury or does not allow natural movements. Option C, loosening clothing, is beneficial but is not the initial priority. The initial response should involve placing the child on his side in the recovery position (to ensure a clear airway and to prevent aspiration) and monitoring the child until the seizure ends.