INDIANAPOLIS -- A grandmother of one of three premature babies who died because of a recent drug overdose at Methodist Hospital told reporters Wednesday that parents of preemies should keep an eye on hospital caregivers.

Joanna Pruitt's granddaughter, Thursday Dawn Jeffers, died late Tuesday at Riley Hospital for Children, where she was taken after receiving an overdose of an anti-clotting drug at Methodist on Saturday.

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Video: Family Of Third Baby Killed By Overdose Asks 'Why?'

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Methodist Hospital officials said Jeffers and five other preemies were accidentally given adult doses of heparin at Methodist's newborn intensive care unit over the weekend. Two of the babies -- 2-day-old Emmery Miller and 5-day-old D'myia Nelson -- died Saturday.

Pruitt, talking to reporters outside the apartment of her daughter, Heather Jeffers -- Thursday Dawn's mother -- said the deaths should be a warning to relatives of preemies: be intimately involved in their treatment.

"Don't just walk away and say, 'I trust you,' because too many people do trust people, and that's what we did. We trusted nurses and doctors to take care of this baby," Pruitt said.

During a moment when she wasn't talking to reporters, Pruitt consoled her daughter, who was sitting outside the apartment and crying.

"She was a beautiful baby. Why did Methodist have to kill my baby? Why?" Jeffers asked her mother as the two hugged.

The three babies who survived the overdoses remained in critical condition at Methodist on Wednesday because they are premature, not because they face any remaining danger from the overdoses, Methodist spokesman Jon Mills said.

Hospital officials said a pharmacy technician accidentally had stored adult dosages of the heparin in the unit's drug cabinet, and that five nurses administered the drug to the babies, not knowing they were using the wrong dosages. The drug prevents blood clots that could clog intravenous tubes.

The hospital said that vials of the adult dosage look similar to those of the dosage that the babies were supposed to have received.

Sam Odle, president and CEO of Methodist Hospital, had said Tuesday that the hospital was offering restitution and counseling for all six of the affected families. He also said Methodist has instituted safeguards to ensure the dosing mistake does not occur again.

Riley Hospital for Children called Heather Jeffers on Tuesday night to inform her Thursday Dawn was nearing death. Pruitt said her daughter told her: "They kept my baby girl alive until I got there. And when I got there, I held my baby girl until she died."'

Pruitt blamed Methodist for Thursday Dawn's death.

"They killed my grandbaby, and I will never forget it and I pray that no one has to go through this," Pruitt said.

Clarian Health Partners, which operates both Methodist Hospital and Riley Hospital for Children, released a statement Thursday morning.

"We are all saddened by this news and our hearts are with the family," the statement read. "We have already implemented measures to ensure that this incident cannot occur again."

At least two of the families -- those of Thursday Dawn Jeffers and Emmery Miller -- have retained an attorney, Nathaniel Lee of Indianapolis. Lee scheduled a news conference for Thursday morning at the law offices of Lee Cossell Kuehn & Love LLP.