A febrile seizure is a fit that can happen when a child has a fever. Febrile seizures are also sometimes called febrile convulsions. They are relatively common and, in most cases, aren't serious. Around one in 20 children will have at least one febrile seizure at some point. They most often occur between the ages of six months and three years. During a febrile seizure, the child's body usually becomes stiff, they lose consciousness and their arms and legs twitch. Some children may wet themselves. This is known as a tonic clonic seizure.