A toddler with proper diarrhoea — six, eight, ten loose stools a day — is exhausting, messy, and can be worrying. The reassuring part: in the under-5 age group, almost all of it is viral gastroenteritis, which gets better on its own in 5–7 days without antibiotics. The actual job of a parent is to keep enough fluid going in to outpace what's coming out, and to know which signs mean you've crossed from "manageable at home" into "needs to be seen". For more on first aid for common childhood illnesses, see Healthbooq.
What's Causing It
In the UK, most acute diarrhoea in children is viral. Rotavirus used to dominate this picture; since the rotavirus vaccine was added to the NHS schedule in 2013 (given orally at 8 and 12 weeks), hospital admissions for severe rotavirus in infants have dropped by around 70%. Norovirus is now the most common pathogen across all ages, and adenovirus, sapovirus, and astrovirus turn up too. Viral gastroenteritis spreads on hands, toys, and shared surfaces — nurseries are a reliable source.
Bacterial causes (Campylobacter, Salmonella, E. coli, Shigella) tend to make a child more obviously unwell, often with higher fever, abdominal cramping, and sometimes blood or mucus in the stool. Food poisoning from staphylococcal toxin shows up fast — vomiting first, often within a few hours of eating, then diarrhoea. Travellers' diarrhoea after a trip abroad and parasitic infections (Giardia) are worth mentioning to the GP.
A child on antibiotics may develop diarrhoea as a side effect. If diarrhoea starts during or shortly after a course, particularly if it's severe or contains blood, the GP needs to know.
Spotting Dehydration Early
This is the part that matters. Children dehydrate faster than adults, and the younger they are, the faster it goes.
Mild dehydration: wet nappies or wee a bit less often, mouth slightly dry, child still alert and playing. Manage at home.
Moderate dehydration: noticeably fewer wet nappies (under 4 in 24 hours in a baby; less than every 6–8 hours in an older child), dry tongue, fewer or no tears when crying, eyes look slightly sunken, the child is grumpy and lacking energy, skin pinched gently on the tummy is slow to spring back. Needs medical review the same day.
Severe dehydration (emergency, call 999 / 111 / go to A&E): no wet nappy in 8+ hours, very dry mouth, deeply sunken eyes, sunken fontanelle in a baby under 12 months, cold or mottled hands and feet, hard to rouse or unusually drowsy, fast breathing, weak cry. This is an IV-fluids situation.
In babies under 12 months the soft spot at the top of the head (anterior fontanelle) is the simplest dehydration check most parents have — sunken means trouble.
Oral Rehydration: Why ORS, Not Water
When the gut is inflamed by gastroenteritis, most absorption goes offline. The one channel that keeps working is the glucose–sodium co-transporter in the small intestine — basically, sodium pulls glucose into the cell, and water follows. ORS (oral rehydration solution) is engineered around exactly this: a precise small amount of glucose plus the right balance of sodium, potassium, and citrate. It is one of the most important medical inventions of the 20th century.
Use: Dioralyte, Electrolade, or supermarket equivalents. Mix one sachet in the exact volume of water specified on the packet. Don't dilute further; don't make it stronger.
Don't use as the main rehydration fluid:
- Plain water — almost no sodium; won't replace losses, can dilute blood sodium in a small child
- Fruit juice — too sugary, can pull more water into the gut and worsen diarrhoea
- Sports drinks (Lucozade Sport, Powerade) — wrong sodium-to-sugar ratio for children
- Fizzy drinks and squash — same problem; high sugar, low sodium
Breastfed babies: keep breastfeeding, on demand and a bit more often than usual. Breast milk is the right fluid for a breastfed baby with gastroenteritis — it provides hydration, calories, and antibodies. Don't stop. Formula-fed babies: keep feeding at normal strength; don't dilute the formula.
How to Actually Get ORS Into a Vomiting Toddler
Big drinks come straight back up. The trick is small and frequent.
NICE recommends 5 mL every 1–2 minutes for an actively vomiting child — that's a teaspoon, or a syringe-full. A 5 mL oral syringe from the pharmacy is the most useful tool here. Set a timer if you need to. Once the child has held it down for 30 minutes, slowly increase the amount.
Aim for roughly 50 mL per kg of body weight over 3–4 hours after a vomiting episode (NICE figure for mild–moderate dehydration), on top of normal fluids. So for a 12 kg toddler, that's about 600 mL over 3–4 hours. In practice, you offer often and accept what they take.
Cold ORS sometimes goes down better than room-temperature. Some children will accept it as ice lollies (freeze the made-up solution in moulds); ice pops are an underrated tool for a vomiting toddler. Flavoured ORS exists; many children dislike all of them, and any ORS that gets in beats none.
If the child point-blank refuses ORS and is mildly dehydrated only, NICE says diluted apple juice or oral rehydration with usual fluids can work in older children — but ORS is the standard.
Food: Don't Starve Them
The old advice to withhold food, then reintroduce slowly with the BRAT diet (banana, rice, apple, toast), is out of date. Both NICE and WHO recommend continuing normal feeding as soon as the child is willing. The gut heals faster when fed.
Plainer carbohydrates — toast, rice, pasta, potato, plain crackers, banana — are easy to eat and well tolerated. Yoghurt is fine and can be helpful. Avoid very fatty or very sugary foods for a few days. There is no need for a special diarrhoea diet.
What Not to Give
- Loperamide (Imodium) — not for children under 12. It can mask deterioration and has been linked to serious complications in young children.
- Antibiotics — not indicated for typical viral gastroenteritis. They are sometimes used for specific bacterial causes (severe Salmonella in an infant, dysentery, confirmed Giardia), but only under medical guidance.
- "Anti-sickness" medicines — generally not given routinely; ondansetron is sometimes used by clinicians in A&E for persistent vomiting, but it's not a home medicine.
- Probiotics — modest evidence; some pharmacies sell them. Cochrane reviews suggest a small reduction in diarrhoea duration, but it's not a substitute for ORS.
When to Get Medical Help
Same-day GP or 111 call if:
- Baby under 3 months with any diarrhoea
- Baby 3–6 months with significant or persistent diarrhoea
- Signs of moderate dehydration (above)
- Six or more diarrhoeal stools in 24 hours, or vomiting that won't stop
- Blood or mucus in the stool
- Diarrhoea lasting more than 7 days
- Fever above 38°C in a baby under 3 months, or above 39°C in an older child
- Child increasingly drowsy, floppy, or "not themselves"
- Recent foreign travel with diarrhoea
999 / A&E if:
- Severe dehydration (sunken fontanelle, no wet nappies in 8+ hours, hard to rouse, mottled skin, unusually fast breathing)
- Bile-stained green vomiting in a baby (possible obstruction)
- Persistent severe abdominal pain
- Seizures or significant confusion
A child whose diarrhoea is settling but who has stopped weeing or has gone unusually quiet has crossed the line from "improving" back to "needs review". Trust that instinct — it's usually right.
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.
