Stomach Bug in Children: Vomiting, Diarrhea, and Dehydration Warning Signs

What Is a Stomach Bug?

The "stomach bug" — properly called viral gastroenteritis — is an infection of the intestines that causes vomiting, diarrhea, stomach cramping, and sometimes fever. Despite being called the "stomach flu," it has nothing to do with influenza. It's caused by viruses that spread quickly through families and daycare settings, making it one of the most common illnesses we treat at Hummingbird Pediatrics in Robbinsville, NJ.

While stomach bugs are uncomfortable and exhausting for both children and parents, most healthy children recover fully within a few days. The primary concern — especially in young children — is preventing dehydration.

What Causes Stomach Bugs in Children?

Several viruses can trigger gastroenteritis in children:

• Norovirus: The most common cause in children over 5 and adults. Highly contagious and can sweep through a school or household quickly.
• Rotavirus: Once the leading cause of severe diarrhea in young children; now much less common thanks to the rotavirus vaccine given in infancy.
• Adenovirus and astrovirus: Other common causes, typically with milder symptoms.

These viruses spread through contaminated food, water, surfaces, and contact with an infected person. They can survive on surfaces for hours to days, which is why stomach bugs spread so readily in families.

Vomiting: What's Normal and What's Not

Vomiting is usually the first symptom of a stomach bug and tends to be the most intense in the first 12–24 hours. What to expect:

• Frequent vomiting every 30–60 minutes in the first several hours is typical
• Vomiting usually subsides significantly within 24 hours
• Some children feel completely fine between vomiting episodes; others feel sick throughout

Vomiting that persists beyond 48 hours without any improvement, contains blood or dark green material (bile), or is accompanied by severe abdominal pain that doesn't go away between episodes warrants a call to your pediatrician.

Diarrhea: How Long Is Too Long?

Diarrhea often starts after the vomiting begins to ease and can last longer — sometimes up to 7–10 days, even in an otherwise typical stomach bug. The key signs to watch for are:

• More than 8–10 loose stools per day in an infant or toddler
• Blood or mucus in the stool
• Diarrhea lasting more than 10–14 days
• Severe abdominal cramping accompanying each episode

Dehydration: The #1 Danger

When children vomit and have diarrhea repeatedly, they lose fluids and electrolytes faster than they can replace them. Dehydration is the most serious complication of a stomach bug — and young children and infants are at highest risk because they have smaller fluid reserves.

Signs of Mild Dehydration

• Mouth and lips that seem drier than usual
• Slightly decreased urine output
• Less active than normal

Signs of Moderate to Severe Dehydration

• No tears when crying
• Dry mouth and sticky saliva
• Significantly decreased urination — no wet diaper in 6–8 hours in infants
• Sunken eyes or sunken fontanelle (soft spot) in infants
• Mottled, cool, or gray skin
• Extreme lethargy — much harder to arouse than usual

Feeding and Fluids: What Actually Helps

Oral Rehydration Solution (ORS)

For children who are vomiting, the best approach is to offer an oral rehydration solution (ORS) such as Pedialyte in small, frequent sips — not large amounts at once. Start with 1 teaspoon every 5 minutes and gradually increase as tolerated. ORS contains the right balance of electrolytes and glucose that plain water does not.

Breastfed Infants

Continue breastfeeding throughout a stomach bug — breast milk provides both fluids and immune support. You may need to nurse more frequently and for shorter periods.

What to Avoid

• Fruit juice and sports drinks: Too high in sugar and too low in sodium — can worsen diarrhea
• Plain water alone for infants: Can dilute sodium levels dangerously in very young children
• Dairy: May worsen diarrhea temporarily due to transient lactose intolerance after a stomach bug
• Fatty or fried foods: Hard to digest during recovery

Reintroducing Food

Once vomiting has stopped for a few hours and your child shows interest in eating, you can begin offering bland, easy-to-digest foods. The old "BRAT diet" (bananas, rice, applesauce, toast) is no longer the AAP's recommendation — it's very low in nutrients and protein. Instead, offer a variety of gentle, low-fat foods that your child tolerates: crackers, toast, soft cooked vegetables, chicken, or whatever they're willing to eat. Return to a normal diet as quickly as your child's appetite allows.

Preventing the Stomach Bug from Spreading

• Frequent handwashing: Wash hands with soap and water for 20 seconds, especially after diaper changes and before preparing food — alcohol-based hand sanitizers are less effective against norovirus
• Disinfect surfaces: Use a bleach-based cleaner on hard surfaces, doorknobs, and faucet handles
• Wash contaminated laundry immediately in hot water
• Keep sick children home until they have been fever-free and without vomiting for at least 24 hours
• Rotavirus vaccine: Given as drops in early infancy, this vaccine dramatically reduces the risk of severe rotavirus gastroenteritis — make sure your baby is up to date

At Hummingbird Pediatrics in Robbinsville, NJ, our board-certified pediatricians are here to help with stomach bugs and dehydration concerns. If you're worried or your child isn't improving, call us at (609) 808-3123 or book an appointment online — we're here to help you navigate even the messiest illnesses.