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A 4-year-old Indiana girl was in critical condition after her 2-year-old brother shot her Thursday, police said.

The children were being watched by their grandparents Thursday morning when the 2-year-old shot his sister once in the head, according to Lebanon police.

The young girl was taken to Indiana University Riley Hospital for surgery, officials said. The state Department of Family and Child Services is assisting in the investigating.

A neighbor, Paula Harvey, told NBC affiliate WTHR that the kids' grandmother watches them often.

"I'm very saddened," Harvey told the station. "This doesn't need to happen. Does not need to happen. Especially to an innocent child."

She added: "Kids are very good. Grandma takes good care of them. She babysits for them, she's a home health care aide. Very quiet people, very good people. Never had a problem with them."