Gastro in babies: vomiting, diarrhea and when to get help

Gastro (gastroenteritis) is an infection of the stomach and bowel. It usually starts with vomiting, then diarrhea, and most babies get better at home with extra feeds and fluids. The main risk is dehydration, and babies under 6 months can get dehydrated quickly, so they need a doctor the same day. This guide covers keeping fluids up, what to avoid, when to get help, how to stop it spreading, and the rotavirus vaccine.

What is gastro and how long does it last?

The Royal Children's Hospital Melbourne (RCH) says many germs can cause gastro, but a virus is the most common, and that gastro is more common and more severe in babies and young children. Australia's healthdirect names rotavirus and norovirus among the viruses, and says gastro can also come from bacteria and parasites.

Gastro spreads through contact with vomit or poop, through contaminated food, drinks or objects such as toys, and, the RCH says, through the air when someone vomits.

The RCH says the first few days are usually the hardest, and that babies may also have a fever, cramping tummy pain that comes and goes, and little interest in feeds. The AAP says a child may vomit everything for the first 3 or 4 hours.

How do I keep my baby hydrated with gastro?

Small amounts often is the key. The RCH says to give small amounts of fluid often, even if your baby is vomiting, and to offer a drink every time they vomit. It also says that even when fluids seem to go straight through, your child still absorbs a lot of what they drink.

The NHS also says to keep breast or bottle feeding, offer smaller feeds more often if your baby is being sick, and never make formula weaker than usual. Australia's healthdirect says a breastfed baby may need to feed more often and can have rehydration fluid between feeds. The AAP says oral rehydration solution is rarely needed in breastfed babies, and suggests shorter, more frequent feeds if a baby vomits more than once.

Giving oral rehydration solution

Oral rehydration solution (ORS) is a drink made to replace the water, sugar and salts lost through vomiting and diarrhea. The Sydney Children's Hospitals Network (SCHN) says it comes as sachets, liquid, tablets, icy poles or ready-to-drink bottles, and to follow the packet instructions closely. The NHS suggests asking a pharmacist to recommend one, and the RCH says you can buy it at supermarkets and pharmacies.

1. Mix it exactly as the packet says. Don't make it stronger or weaker.
2. Give a little at a time. A spoon, cup or medicine syringe (no needle) helps. The RCH suggests a syringe for a very young child who won't drink.
3. Go slowly for babies 6 to 12 months who aren't feeding normally. The RCH dehydration fact sheet suggests about 5 mL by syringe every 5 minutes while they're awake, for 4 hours, then seeing a doctor if they aren't improving or can't keep anything down.
4. Expect some resistance. The RCH says many children don't like the salty taste; ORS icy poles can be easier.
5. Water for young babies. The RCH says babies under 6 months get their fluids from breast milk or formula and don't need water. The NHS suggests small sips of water between feeds for babies on formula or solids. See water for babies.

Which drinks and medicines should I avoid?

Sugary drinks. The RCH says lemonade, ginger ale, sports drinks and fortified feeds are high in sugar and can make dehydration worse. Lemonade left to go flat still has all its sugar. The NHS and the AAP say to avoid fruit juice and fizzy drinks, which can make diarrhea worse.

Sources differ on diluted juice. For children from 6 months who won't take ORS, the RCH suggests half-strength apple juice mixed with water, and Australia's healthdirect suggests 1 part juice to 4 parts water. ORS is the better choice, and full-strength juice is best left out. See juice for babies.

Medicines to stop vomiting or diarrhea. The RCH says over-the-counter medicines that reduce vomiting and diarrhea may be harmful for children, and Australia's healthdirect says not to give anti-diarrhea medicines to children. A doctor may prescribe an anti-nausea medicine for severe vomiting.

Pain and fever medicine. The RCH says acetaminophen can help with pain, and not to give aspirin. Follow the label or ask a pharmacist. The NHS fever page says not to give ibuprofen to a child who is dehydrated, or to a baby under 3 months.

Antibiotics. The RCH says doctors rarely use them, even for bacterial gastro, because most children get better without them.

What if my baby is under 6 months?

Young babies have less in reserve. The RCH says babies under 6 months are at higher risk of dehydration and should see a doctor or health professional if they show signs of gastro. Australia's healthdirect says to take a baby under 6 months to a doctor if you think they have gastro, and SCHN says to keep feeding and get your baby seen as soon as possible. The AAP says to call the doctor straight away if a baby under 12 weeks vomits 2 or more times.

Keep breast or formula feeds going while you arrange to be seen. For a baby under 3 months, any temperature of 38°C (100.4°F) or more means calling 911 or going straight to the emergency room. Australia's healthdirect also says a young child with gastro should see a doctor if they weigh less than 8 kg, were born prematurely or have other health problems.

When can my baby eat normally again?

The RCH says there are no specific food rules during or after gastro: let your child's appetite guide you, and offer food again once vomiting has stopped and they feel less sick. It says the bowel heals more quickly with food in it, and that refusing food at first isn't a problem if they're drinking enough. SCHN suggests holding off solids while your baby is vomiting, then offering simple foods even if poop is still runny.

The RCH says some children can't digest dairy sugar (lactose) properly for a while after gastro, which causes wind and acidic diarrhea. In older children it suggests cutting back dairy for around three weeks. Don't change your baby's formula without talking to your doctor or pediatrician first. For what runny poop looks like, see baby poop.

How do I stop gastro spreading?

Gastro spreads easily through a household. The NHS, the RCH and Australia's healthdirect suggest:

• washing your hands well with soap and water after diaper changes, after cleaning up vomit or diarrhea, and before feeding your baby or preparing food
• washing soiled clothes and bedding separately on a hot wash
• cleaning toilet seats, flush handles, taps and shared surfaces every day, and washing or disinfecting toys
• wearing gloves when cleaning up vomit or poop, and bagging paper towels before throwing them out
• not sharing towels, face washers, cups or cutlery
• not preparing food for other people while you're sick yourself

Childcare. The RCH and the NHS both say your child can go back to childcare once they're well and have had no vomiting or diarrhea for 48 hours. The NHS says to stay out of swimming pools for at least 48 hours after symptoms stop, and the RCH says 2 weeks. See starting childcare.

Does the rotavirus vaccine prevent gastro?

Rotavirus is a common cause of severe gastro in babies and young children, and a vaccine given as drops in the mouth protects against it. It won't prevent gastro from other germs, so hygiene still matters.

The NSW Health schedule lists the Australian National Immunization Program doses. The NHS rotavirus vaccine page says the vaccine prevents rotavirus infection in about 8 out of every 10 babies, and the CDC says about 9 out of 10 vaccinated children are protected from severe rotavirus disease. In the US, the AAP explains that the CDC removed rotavirus vaccine from its routine schedule in January 2026, but the AAP still recommends it, so ask your pediatrician.

The NHS says the most common side effects are diarrhea and irritability, and that there's a very small risk of a bowel blockage (intussusception) in the week after a dose. It also suggests washing your hands well after diaper changes for a few weeks, as poop can contain the weakened vaccine virus. Because of the age limits, ask about a catch-up soon if a dose is missed. See vaccinations.

When to get help

Signs can change quickly in a baby with gastro, so keep checking, including overnight. These tiers match our dehydration signs and when to call the doctor guides. If you're unsure, call your pediatrician's after-hours nurse line.

Call 911 now if your baby:

• has green or yellow vomit
• vomits blood, or has red, black or brown vomit or vomit that looks like coffee grounds
• is vomiting and has a swollen, hard or tender tummy, or has a sudden, severe tummy ache
• has more than a streak of blood in their poop together with vomiting, a swollen tummy, or is pale, floppy or very unwell
• has sunken eyes or a sunken soft spot, cold or mottled hands and feet, or is very sleepy
• has only 1 or 2 wet diapers in a day, or has had no wet diaper or pee for 12 hours
• can't keep any fluids down and has several signs of dehydration
• is floppy, much sleepier than usual, hard to wake, can't be woken or isn't responding as usual
• is struggling to breathe, or has blue, gray, very pale or blotchy skin, lips or tongue
• has a stiff neck, a rash that doesn't fade under a glass, or a seizure
• is under 3 months and has a temperature of 38°C (100.4°F) or higher, or is 3 to 6 months old and has a temperature of 39°C (102.2°F) or higher

SCHN says green or yellow vomit can mean a blocked or twisted bowel, and that babies can look healthy while the bowel is being damaged. The NHS lists green or yellow-green vomit, vomiting blood and a sudden, severe tummy ache among reasons to call an ambulance or go to A&E. The RCH says khaki-green vomit needs hospital and yellow vomit is usually not a concern; we use the stricter tier. NICE says a swollen or tender tummy can suggest a blocked bowel, and the NHS reflux page gives a swollen tummy an urgent doctor appointment; with vomiting, we use the emergency tier. The RCH sends severe dehydration, and a child who can't keep fluids down with several dehydration signs, to hospital, and the NHS urgent-help guide lists no pee for 12 hours among reasons to call an ambulance. If your baby is alert and breathing normally, going straight to the nearest emergency room for green vomit or severe dehydration is fine.

Get medical help today (same-day doctor, after-hours doctor or your pediatrician's after-hours nurse line) if your baby:

• is under 6 months and has vomiting, diarrhea or a fever (use the emergency tier for fever under 3 months)
• has fewer wet diapers, darker pee, a dry mouth or fewer tears
• keeps vomiting and can't keep fluids down, or has been vomiting for 24 hours
• is refusing feeds, feeding much less than usual, or has stopped breast or bottle feeding
• has blood in their poop; the RCH says this is common with gastro and rarely serious, but it should be checked
• has a lot of watery poops (the RCH says 8 to 10 a day) or diarrhea lasting more than 7 days
• has tummy pain that is constant rather than coming and going, or is getting worse
• isn't improving after 4 hours of extra fluids, or still has dehydration signs after ORS
• has had a temperature for 5 days or more, or has a long-term heart, kidney or bowel condition

Talk to your doctor or pediatrician if your baby picked up gastro overseas, which the RCH says to discuss with a doctor, if runny poop keeps coming back after dairy, or if you'd like a plan for next time, such as which ORS to keep at home.

What's worth noting while your baby has gastro?

Note each vomit and runny poop with the time, every feed or drink (even small ones), and wet diapers. Runny poop can make it hard to tell if a diaper has pee in it, so say so when you call. Write down any medicine with the time and, if you can, take a photo of unusual vomit or poop to show the doctor. Never delay getting help to finish a note.