She handed the Class A drug in to security services and laid a formal complaint with the hospital's management, her partner said.
Allan Trow said the incident happened three days ago and had upset him and his partner.
''Kids run up and down those wards. What if one of them picked up that bag up and swallowed its contents? It could kill them,'' Trow said.
''What kind of people take P into a children's ward in a hospital? If you're going to do that stuff, leave it at home.''
Northland District Health Board (NDHB) confirmed a complaint about the alleged find was received by mail yesterday afternoon.
It would be investigated, as per the normal procedure when a complaint was laid, but it had only just been formally notified. The NDHB could not confirm at this stage if or when the police would become involved.
Before NDHB had the complaint in hand, Northland Police told the Northern Advocate they were unaware of the P allegation.
Trow said the incident came on top of other concerns he and his partner had about security and safety in the children's ward.
They included the daily theft of food, milk, tea, coffee and drinking chocolate, and even takeaway cups from the kitchen. Named containers disappeared from the fridge and other items went missing from the ward, he said.
His partner had many wakeful night hours because of their baby's feeding problems and needed her hot drinks to keep her going, he said.
When visitors pressed the admission button, staff operated the buzz-in system from the nurses' desk so there were few checks on who or how many people came in, Trow said.
Sometimes large numbers of visitors at one bed in a room of four patients were very noisy or took up all the room.
''The nurses are that bloody busy they shouldn't have to take on more pressure. They need to have security guards or at least more CCTV monitors on those wards.''
After visiting his partner and baby one evening this week, Trow and their two other young sons passed three men outside the hospital's main door who were openly talking about a drug deal, he said.
Posts Trow put on social media have attracted accounts of similar experiences of food thefts and other bad behaviour at the hospital.
The NDHB said it would not comment on other issues raised or the negative activity on social media following Trow's posts.
