Diarrhoea is one of the most common reasons parents seek medical advice in the under-5 age group. The large majority of cases are caused by viral gastroenteritis – a self-limiting infection that requires no antibiotic treatment and resolves within a week. What matters is keeping the child adequately hydrated while the illness runs its course.
Healthbooq covers children's health and first aid for common childhood illnesses.
Causes of Diarrhoea in Young Children
Viral gastroenteritis accounts for the majority of acute diarrhoea in young children. Rotavirus was historically the most common cause in the UK, producing the characteristic profuse, watery, foul-smelling diarrhoea in young infants; since the introduction of the rotavirus vaccine into the NHS schedule in 2013, rotavirus-related hospitalisations in infants have fallen by approximately 70%. Norovirus is now among the most common causes in all age groups.
Bacterial gastroenteritis (Campylobacter, Salmonella, E. coli, Shigella) tends to produce more severe symptoms including fever and sometimes bloody stool. Food poisoning (Staphylococcus aureus toxin) typically causes rapid-onset vomiting with diarrhoea following.
Assessing Dehydration
Dehydration is the primary clinical risk of diarrhoea. The signs of dehydration in children range from mild to severe:
Mild dehydration: normal or mildly reduced urine output, slight mouth dryness, the child is alert and active.
Moderate dehydration: reduced urine output, dry mouth and eyes, reduced skin turgor (skin springs back more slowly when gently pinched), mild sunken eyes, the child is irritable.
Severe dehydration: significantly reduced or absent urine output, very sunken eyes, very dry mouth, absent tears, pale or mottled skin, markedly reduced responsiveness. This requires emergency assessment.
In young infants, the fontanelle (the soft spot at the top of the skull) may become sunken with dehydration.
Oral Rehydration: What to Use
The most important principle of diarrhoea management in children is oral rehydration with the correct fluid. Oral rehydration solution (ORS) is a carefully formulated mixture of electrolytes and a small amount of glucose in water. The glucose-sodium co-transport mechanism in the small intestinal wall is one of the few mechanisms that remains functional during diarrhoeal illness and allows sodium and water to be absorbed alongside glucose.
ORS sachets (Dioralyte, Electrolade) should be dissolved in the exact amount of water specified on the packet. The solution should not be diluted further.
What NOT to use for rehydration:- Plain water: insufficient sodium and electrolyte content
- Fruit juice: too high in sugar, insufficient electrolytes, may worsen diarrhoea
- Sports drinks: incorrect electrolyte composition for children
- Fizzy drinks: inappropriate sugar and electrolyte balance
Breastfed infants: breastfeeding should continue throughout diarrhoeal illness. Breast milk continues to provide hydration and immune support.
How to Give ORS to Young Children
Children with vomiting as well as diarrhoea may struggle to retain oral fluids. Small, frequent amounts are more likely to be retained than large volumes. NICE guidance for mild-to-moderate dehydration recommends giving ORS in 5ml aliquots every 1-2 minutes in actively vomiting children, with the volume increased as tolerance improves.
For most children with mild diarrhoea and no significant vomiting, offering ORS freely alongside normal fluids (and continuing breastfeeding) is appropriate.
Continuing Food
Withholding food during diarrhoeal illness is outdated advice. NICE guidance and WHO recommendations both support continuing normal feeds and food as soon as the child is willing to eat. Starchy foods (toast, rice, potato) are easy to eat and do not worsen diarrhoea. There is no clinical basis for restricting diet to "bland" foods or for the traditional "BRAT diet" (banana, rice, apple, toast).
When to Seek Assessment
Medical assessment is appropriate if:
- The child is under 3 months with any diarrhoeal illness
- Signs of moderate or severe dehydration are present
- Blood or mucus is present in the stool
- Diarrhoea persists beyond 5-7 days without improvement
- The child has a high fever (above 38°C in under-3 months; 38.5°C in older children with other concerning features)
- The child cannot keep down any fluids despite small, frequent attempts
- The child is becoming increasingly unwell
Key Takeaways
Diarrhoea in young children is most commonly caused by viral gastroenteritis (rotavirus, norovirus) and is self-limiting. The primary risk is dehydration. The cornerstone of management is oral rehydration: using oral rehydration solution (ORS, such as Dioralyte) to replace lost fluids and electrolytes. Plain water, fruit juice, and sports drinks are not appropriate as they do not have the correct electrolyte composition to replace losses. Breastfeeding should continue throughout diarrhoeal illness. Antidiarrhoeal medicines (loperamide) are not appropriate for children under 12. Most cases of simple gastroenteritis in children resolve within 5-7 days.
