Small children and babies vomit more easily than you and your partner when they're ill. Vomiting once at the beginning of an illness is common and requires no special treatment, but repeated vomiting requires medical evaluation because of the risk of dehydration.
Signs of serious dehydration require medical treatment. A sunken fontanel (the soft spot on the top of an infant's head), extreme lethargy, sunken eyes, or sunken skin that remains raised after you pinch it deserve an immediate call to the baby's doctor.
Pediatricians often recommend giving vomiting children younger than six months an oral balanced-electrolyte solution such as Pedialyte in place of formula, starting with a few teaspoons or half an ounce every 15 minutes or so.
Don't give plain water to any child younger than 1 unless your pediatrician specifically recommends it. A medication syringe often works better than a spoon for giving fluids if your baby refuses to drink. Gradually increase the amount you give each time if the baby isn't vomiting it back up.
Don't give a volume more than you normally would. For example, if you normally give 4 ounces of formula every four hours, don't exceed that amount.
If no vomiting occurs after 12 hours, slowly start to reintroduce formula, but stop if vomiting occurs again. Breast-fed babies should continue to nurse because breast milk is more digestible than anything on the planet. However, if vomiting continues, call your doctor.
Some medical personnel recommend following the BRAT (bananas, rice, applesauce, and toast) diet during and after a vomiting illness for children older than 1, after they haven't vomited for eight hours or so, because these foods are easily digested. Others say to give children whatever they want and can keep down. Either way, go slowly and don't introduce any new foods until all vomiting and stomach upset have passed.
Babies who suddenly start vomiting after every feeding even though they appear healthy and still have an appetite may have pyloric stenosis, a narrowing between the stomach and small intestine. Pyloric stenosis requires surgery but has no aftereffects; when it's fixed, it's fixed.