Baby-Sitter, 15, Is Arrested in Infant’s Death : Investigation: Police are basing their suspicions on the injuries to baby and 4-year-old’s brother’s contention that he saw the teen-ager abusing the child.

SANTA ANA —  Police Tuesday arrested a 15-year-old girl for allegedly killing an infant under her care after the baby boy’s older brother told authorities that he saw the baby-sitter abusing the child.

Oscar Vargas, 9 months old, of Santa Ana died late Monday night of blunt force, caused by either a hand or a fist, and severe shaking, Police Lt. Bob Helton said.

Paramedics were called to the house by parents when they returned home from work at midnight, but the infant appeared to have died of internal bleeding several hours earlier, Helton said.

“The initial investigation indicates that . . . sometime in the evening on Monday, (the baby) sustained severe trauma while in the care of the baby-sitter,” Helton said.

Police investigators declined to identify the baby-sitter because of her age. She is being held without bail in Orange County Juvenile Hall on suspicion of murder, pending a court hearing which will decide whether she should face charges, Helton said.

Helton said that it was extremely rare to accuse a baby-sitter of murder.

“I cannot recall how long it’s been, if ever, since we had a case like this,” Helton said.

Child-care experts said the child’s death, whether through negligence or other causes, underscores the constant dilemma that working parents face. They must find affordable care for their youngsters in an unregulated field, and they are often ill-equipped to adequately screen perspective employees, experts said.

Rogelio, 26, the boy’s father, said he was numb with shock over the sudden loss of the youngest of his three children.

“I never expected anything like this,” he said, when three weeks ago he hired the teen-ager, a recent immigrant from Mexico, on the recommendation of her family. Vargas said he and the boy’s mother, Maria Eusebio, 22, both work until midnight at a local electronics store.

The couple had returned home, in the 1000 block of East Washington Avenue, where the teen-ager was left to care for Oscar and Rogelio and Diana, 2, the couple’s other two children.

Vargas said he did not know the teen-ager well. “I have known her family for a long time,” Vargas said in Spanish, adding that the teen-ager was living with the family five days a week. It was not clear where she lived during the weekends and whether she attended school.

“When we came home, the baby was dead . . . in the crib,” Vargas said Tuesday afternoon as he stood in the small front yard of his modest home. His eyes were red from lack of sleep.

Vargas and Eusebio, frantic that the baby was dead, called 911 and questioned the baby-sitter. They were initially told by the teen-ager that the baby fell off his walker and that’s what had caused bruises on his buttocks, a torn lip and a swollen face.

She also told them that the baby appeared to have died around 10:30 p.m., but she did not call authorities, Vargas said.

“By the way the baby looked, we think that she hit him,” he said. “(Oscar) had never fallen (from the walker) before. He was small, and he could not jump. He was just beginning to use the walker.”

When police and paramedics arrived, Helton said, the baby-sitter “denied any knowledge about how the baby could have been injured.”

However, Vargas’ 4-year-old son, Rogelio Jr., told police that the baby-sitter had hit the baby, Vargas said. Helton could not confirm that.

Vargas said he had noticed that the teen-ager frequently lost patience with his three children, especially Oscar, and now regrets not having cautioned the baby-sitter and paid more attention to the situation.

“At times she would scream at him,” he said.

Janet Shannon, executive director of the International Nanny Assn., based in Austin, Tex., said the death is “the kind of thing that makes your blood run cold.” It is especially troublesome on the heels of a child’s death in New York, in which a 20-year-old Swiss au pair was accused of murder and arson after the 2-year-old she was caring for died in a house fire in Thornwood. Au pairs are usually foreign nannies who trade their services for room, board and pay.

Professionals in the field are also shaking their heads about the current movie, “The Hand That Rocks The Cradle,” which portrays a deranged live-in who appears perfect but turns on the mother in a bloody confrontation.

“Parents are nervous anyway. Fiction plus a match with reality makes it really difficult for parents,” Shannon said. “They still have to go to work. They still need child care. I can understand why they are terrified.”

Of about 20 million children under 5 years of age, an estimated 800,000 are cared for at home by non-relatives, she said. Some care-givers are trained nannies, some are au pairs , and a vast, unknown number are illegal immigrants--a popular choice in Orange County, where some baby-sitters will work a six-day week for $100.

The industry is unregulated, and parents should be diligent in checking references and observing how prospective care-givers act with their child, experts said. Referral agencies should also be checked out, they said. Most agencies said they do not refer anyone under 18 years of age.

“It’s not enough anymore that the person seems nice,” Shannon said.

In interviewing applicants, parents should ask whether the person thinks it’s ever OK to hit children, said Alison Clarke-Stewart, professor of social ecology at UC Irvine. “If they say yes, then you don’t want them.”

Times staff writer Gebe Martinez contributed to this report.