There was no obvious signs of trauma to the children; "Investigators will interview the parents as they try to piece together what caused this tragedy," Phoenix PD said in their initial statement.
In a press conference late on Monday night, Sgt. Mercedes Fortune said officers had been told the children had been ill earlier that day, and that may have been the cause.
"We're trying to determine why this occurred," she added, per AZFamily. "Any time you have three children that are deceased ... in that aspect, it is suspicious."
UPDATE: Mom arrested, admits to killing kids ages 3, 2 and 7 months. Mom is a 22-year-old woman who recently moved to Arizona from Oklahoma. Crime happened in their home near 24th Street and Vineyard pic.twitter.com/iqCivZ66jZ