The mouth and nose are two organs of the human body used for breathing. Normally, breathing is done through the nose, but when the nose is blocked, mouth breathing occurs. Therefore, mouth breathing is a sign of respiratory discomfort and nasal congestion. Common causes like acute and chronic rhinitis, upper respiratory infections, enlarged tonsils, enlarged adenoids, and nasal foreign bodies can all lead to children sleeping with their mouths open. Thus, a child sleeping with an open mouth does not necessarily indicate enlarged adenoids. If a child experiences nasal congestion, snoring, or mouth breathing for more than a month, it is advisable to consult an otolaryngologist (ENT specialist) for a timely examination.