Bags of intravenous fluid have been found punctured in a storeroom at a paediatric ward of an Essex hospital.
Staff at Basildon University Hospital called police on Sunday after more than 30 bags were found damaged in what police believe may be a deliberate act.
Police said staff would be interviewed and cctv
is being examined. The store room has been sealed off while forensic examinations take place.
The hospital trust said concerned parents should call 01268 598536.
Maggie Rogers, director of nursing at Basildon and Thurrock University Hospitals NHS Foundation Trust, said: "I can reassure our local community that we rapidly took necessary steps to ensure patient safety."
Essex Police appealed for anyone with information to contact police. the bbc