Final answer:
The best treatment option for a child with new onset of urticaria is Benadryl, an antihistamine that provides immediate relief by blocking the actions of histamine, a chemical responsible for allergic reaction symptoms.
Step-by-step explanation:
The recommended treatment option for a child with new onset of urticaria, also known as hives, would be antihistamines like Benadryl (diphenhydramine). This medication works by blocking histamine, a substance in the body that causes allergic symptoms like itching and swelling. While calamine cream can soothe itching, it may not be as effective for allergic reactions. Mupirocin is an antibiotic and not suitable for treating hives. Hydrocortisone cream is a corticosteroid that can reduce inflammation and may be used to help with itching and rashes; however, for immediate relief of symptoms, Benadryl is often the first choice for treatment.