The incident occurred shortly before 2:00pm today at the three-star, 25-bedroomed Quality Hotel, Redbarn, Youghal, in east Co. Cork.
The boy and his family were understood to be in the leisure centre swimming pool when the boy got into difficulty.
The boy, who was on holidays with his family, was taken from the water by two lifeguards who administered CPR before he was immediately airlifted to Cork University Hospital by the Waterford-based Coast Guard helicopter.
The four-year-old has since been transferred to the Children’s University Hospital, Temple Street, Dublin, this evening.
Gardaí are investigating, however the incident is being treated as an unfortunate workplace accident.