They can't keep anything down

Small and often beats normal

A stomach that has just emptied itself rejects a full cup almost reliably, and the resulting vomit loses more fluid than the drink replaced. Very small amounts very frequently is the approach that works — a teaspoon or two every few minutes, building slowly once it stays down.

An oral rehydration solution is designed for this and is better than water, juice or sports drinks, which have the wrong sugar and salt balance and can worsen diarrhoea. For a breastfed baby, continuing to nurse in shorter, more frequent feeds is the right version of the same idea.

What to watch instead of the count

Wet nappies or trips to the toilet are the single most useful measure. Tears when crying, a moist mouth, and normal alertness are the others.

The concerning picture is the opposite: no wet nappy for many hours, a dry mouth, no tears, sunken eyes or a sunken fontanelle in a baby, and unusual sleepiness or floppiness. A child who is drinking and weeing is winning, however dramatic the last hour looked.

Food, and the advice that has changed

The old BRAT diet — bananas, rice, apple, toast — is no longer the recommendation. It is unnecessarily restrictive and low in protein and fat.

Once vomiting has settled, returning to a normal age-appropriate diet is what is now advised, and it shortens recovery rather than prolonging it. Appetite will be poor for a while; that is expected and not something to push against.

When it stops being a waiting game

Call for green or bright yellow vomit, blood in vomit or stool, a hard or swollen belly, or severe pain that stays in one place.

Forceful, projectile vomiting after feeds in a baby between roughly two and eight weeks has a specific and treatable cause worth ruling out promptly rather than watching.

Also call for signs of dehydration, a child who cannot be roused properly, vomiting after a head injury, or a bug that simply is not turning around after a couple of days.