A Phoenix woman has been arrested on suspicion of killing her three children, who were found dead inside the family's home, authorities said Tuesday. The 22-year-old mother, identified as Rachel Henry, "has admitted to harming her three children, which caused their demise," police Sergeant Mercedes Fortune told reporters outside the home.

"We are comfortable in saying now that the mother is responsible for the death of the children," Fortune said. Henry was booked on three counts of first-degree murder.

There was no information on whether she had an attorney who could speak on her behalf. A relative who lives at the residence called police late Monday; Fortune said two other adults lived at the residence in addition to the parents, CBS affiliate KPHO-TV reports.

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Responding officers found a 7-month-old girl, 2-year-old girl and 3-year-old boy in a living room area, authorities said. The children were unresponsive and pronounced dead after officers administered CPR and fire officials provided first aid.

Police were interviewing the 30-year-old father and a 49-year-old relative who lives in the home, according to authorities. There was no obvious trauma to the children, and relatives initially believed illness may have been a factor, police said.

It's too early to determine how the children died, police said. The investigation remains ongoing.

A makeshift memorial of three white candles was seen near the house. It's in a neighborhood with old homes of wood or stucco, and a white Spanish-style church graces a corner.

But new construction is going up all around, with a golf course and several housing developments of single-family homes priced at more than $500,000.