Otitis media with effusion (OME) is a common condition in which fluid collects behind the eardrum without signs of infection. It can cause hearing problems and discomfort. Many children get better with medication, but in some cases, the condition becomes long-term and may require surgery. OME is caused by dysfunction of the Eustachian tube, which helps balance the air pressure between the middle ear and the back of the nose (nasopharynx). Restoring proper airflow to the middle ear is important. In addition to medication, physicians often recommend pressure-based exercises such as balloon-blowing, swallowing exercises, the Valsalva maneuver, or chewing gum. These exercises help open the Eustachian tube by creating positive pressure in the nasopharynx, which can improve ear ventilation and reduce symptoms by relieving negative pressure in the middle ear. This study will test the effect of a breathing exercise device called AirOFit PRO™ (AirOFit, Copenhagen, Denmark) in children with OME. Currently, there are no studies in the medical literature showing whether AirOFit PRO™ is effective in treating OME. If this study finds that using the AirOFit PRO™ helps children recover more quickly, it could be an important step in preventing chronic OME and reducing the need for surgery.