"What should I do to help my 21-month-old son struggling with gastroenteritis?"

To help your 21-month-old son with gastro symptoms, focus on rehydrating him using a commercial oral rehydration solution or a homemade recipe. Start with small amounts and gradually increase if he keeps it down. Introduce easily digestible foods when vomiting subsides. Monitor for signs of dehydration and seek medical help if necessary. Use acetaminophen for fever, considering suppositories if he vomits the medication. It's key to prioritize rehydration and respond to your child's overall condition.