**Core Concept**
Rotavirus gastroenteritis is a common cause of severe diarrhea in infants and young children worldwide. The clinical presentation of rotavirus infection typically includes watery diarrhea, vomiting, and fever.

**Why the Correct Answer is Right**
The correct answer is based on the clinical presentation of the child, which is consistent with rotavirus gastroenteritis. The presence of watery diarrhea, vomiting, and fever in a 4-month-old child is highly suggestive of rotavirus infection. The management of rotavirus gastroenteritis involves fluid replacement and electrolyte management to prevent dehydration. The use of oral rehydration therapy (ORT) is the mainstay of treatment in children with rotavirus gastroenteritis.

**Why Each Wrong Option is Incorrect**
**Option A:** Administering antibiotics would not be effective in treating rotavirus gastroenteritis, as it is a viral infection. Antibiotics are only effective against bacterial infections.
**Option B:** Stopping breastfeeding would not be recommended, as breast milk provides essential nutrients and antibodies that help protect against infections.
**Option C:** Administering anti-diarrheal medications such as loperamide would not be recommended, as they can prolong the duration of diarrhea and increase the risk of complications.

**Clinical Pearl / High-Yield Fact**
It's essential to diagnose and manage rotavirus gastroenteritis promptly to prevent dehydration and electrolyte imbalances in young children.

**Correct Answer: D. Oral rehydration therapy (ORT) and supportive care.**