The website healthychildren.org has a discussion on how to stop a child’s nosebleed. A nosebleed usually comes on suddenly, with blood flowing freely from one nostril. Most nosebleeds stop by themselves within a few minutes.
The first step is to stay calm as the nosebleed is probably not serious and you don’t want to upset your child. Your child will pick up on your emotions and become anxious. Keep your child sitting or standing up so the blood will flow out the nose and not down their throat, which might make them vomit.