See Daily Mail report.
GP receptionist made out a prescription for the baby, but disregarded the warning given by the computer that the dose was too high, and then presented it to the doctor as though it was a repeat prescription, which it wasn't. The doctor signed the prescription without noticing the error. The pharmacist dispensed it without checking that his technician had spoken to the doctor about the dose. And the innocent mother therefore administered ten times the correct amount of the powerful diuretic Furosemide to her poorly baby. At every stage of this catalogue of avoidable, careless errors, there were procedures/protocols in place to prevent just such mistakes, but they were ignored/disregarded - even overridden(!) by the receptionist - and a baby died.
I believe these mistakes happen because any punishments that ensue to the professionals who make the mistakes are too light. If they knew that making a serious mistake would bring them a serious punishment they would take far more care to avoid making the mistakes and far more care to follow recommended procedures.