Vomiting in children is most often caused by a viral tummy bug (gastroenteritis) and usually settles within a day or two. The main aim is to prevent dehydration: offer small amounts of clear fluid or an oral rehydration solution every few minutes rather than large drinks, which can trigger more vomiting. Continue breast or bottle feeds for babies, offered little and often.
Contact a doctor or seek urgent care if your child cannot keep any fluids down, shows signs of dehydration (no wet nappies, dry mouth, sunken eyes, drowsiness), vomits blood, brings up green or yellow-green (bile-stained) vomit, has severe or worsening tummy pain, or has a swollen, tender abdomen. These can point to problems that need prompt assessment.
Also seek help if vomiting follows a head injury, comes with a stiff neck or a non-fading rash, or persists beyond a day or two. Avoid giving anti-vomiting medicines to children unless a doctor advises it.