A ward at the Royal Hospital for Children has been closed to new admissions after four patients tested positive for rotavirus.
Extra infection control precautions have been put in place and visitors are being reminded of the importance of hand hygiene when entering and leaving the hospital.
A health board spokesperson said: “Rotavirus is the most common cause diarrhoeal disease among infants and young children, but older children and adults also can get sick from rotavirus.
Once a person has been exposed to rotavirus, it can take up to two days for the symptoms to appear.
Children who get infected may have severe diarrhoea, often with vomiting, fever, loss of appetite and abdominal pain. Vomiting and diarrhoea can last from there to eight days.