A stomach bug in a baby or toddler — with its sudden vomiting, frequent loose stools, distress, and disruption — is one of the more alarming experiences of early parenting, particularly the first time. Most cases are caused by common viral infections that run their course within days, but the management matters — particularly around fluid intake — because dehydration in young children can develop quickly and require medical intervention.
Understanding what to expect, how to manage fluids, when the situation calls for a GP visit, and when it is a true emergency helps parents navigate this common illness with appropriate action rather than either panic or dismissal.
Logging the timeline of symptoms — first vomiting, frequency of loose stools, last wet nappy, any temperature — in Healthbooq gives you accurate information for a healthcare professional if you need to call for advice.
The Typical Course
Viral gastroenteritis typically begins with sudden vomiting, which may be frequent and forceful in the first twelve to twenty-four hours and then reduces in frequency. Diarrhoea usually begins within the first day, often persisting for several days after vomiting has resolved. Total illness duration is typically three to seven days for the acute phase, though loose stools can persist for two weeks in some children.
A mild fever (below 38.5°C) is common. The child may be irritable and have reduced appetite, both of which are expected and do not require separate intervention.
Rotavirus — the most common cause of severe gastroenteritis in infants — produces watery green stools and can cause more significant vomiting. The rotavirus vaccine, introduced in the UK national schedule in 2013, has substantially reduced hospital admissions for severe rotavirus gastroenteritis in vaccinated cohorts.
Managing Fluids
Maintaining adequate hydration is the central task of managing gastroenteritis. For breastfed babies, the most important guidance is to continue breastfeeding through the illness — do not withhold breast milk. Breast milk contains antibodies that support recovery and is the optimal fluid for a breastfed infant with gastroenteritis. Offer more frequent feeds than usual.
For formula-fed babies, formula feeds should be continued. Do not dilute formula.
For babies and toddlers who are vomiting and having difficulty keeping fluids down, oral rehydration solution (ORS — such as Dioralyte) is more effective than water, juice, or sports drinks at replacing the electrolytes lost through vomiting and diarrhoea. ORS should be offered in small, frequent amounts — five to ten ml every five minutes — which is better tolerated than larger volumes. Water alone is not appropriate as the primary rehydration fluid in significant gastroenteritis because it does not replace the sodium and electrolytes lost.
Avoid fruit juices and fizzy drinks, which can worsen diarrhoea and are not appropriate rehydration fluids.
Signs of Dehydration
The most important clinical task in managing gastroenteritis is monitoring for dehydration. Key signs:
Mild dehydration: fewer wet nappies than usual, slightly dry mouth, less active than usual but still alert, no tears when crying.
Moderate dehydration: significantly fewer wet nappies (fewer than two to three in twenty-four hours), dry mouth and tongue, lethargy, eyes appearing slightly sunken.
Severe dehydration: no wet nappies in more than eight hours, very dry mouth, sunken eyes and sunken fontanelle (the soft spot on a baby's head), marked lethargy or difficulty being roused, cold or mottled skin. This requires emergency medical care.
When to Seek Medical Advice
Seek medical advice promptly for:
- Any baby under three months with vomiting and/or diarrhoea
- Signs of moderate or severe dehydration
- Vomiting that is persistent and bile-coloured (yellow or green) in a young infant — this can indicate intestinal obstruction rather than gastroenteritis
- Blood or significant mucus in the stool
- Fever above 39°C
- Symptoms that are worsening after two days rather than improving
- A parent who is not confident the child is maintaining adequate fluids
Key Takeaways
Gastroenteritis (diarrhoea and vomiting) is very common in babies and young children and is usually caused by a virus, most often rotavirus or norovirus. Most cases resolve within three to seven days without specific treatment. The primary management is preventing dehydration — maintaining adequate fluid intake, using oral rehydration solution (ORS) when vomiting is significant, and continuing breastfeeding. Babies under three months with gastroenteritis should be seen promptly by a healthcare professional. Signs of dehydration — reduced wet nappies, dry mouth, sunken fontanelle, lethargy — warrant medical assessment at any age.
