RIVERVIEW — In a house full of children, silence means only one thing to Marie Cherubin: Something's not right.A foster mom of special needs children for 16 years, Cherubin, 59, has spent her days learning the language of children who cannot speak. Children with Down syndrome, Fragile X syndrome and autism.Children like Arriyanna Pivacek, an energetic 10-year-old with autism who would sing and hum and squeak and chirp from the moment she woke up until the moment she went to sleep.The house is quieter now.Arriyanna drowned Saturday afternoon in a small neighborhood pond after wandering away from a birthday party at the home of a family that had been trying to adopt her.It took eight adults at the party and about 50 sheriff's deputies, including canine units, a helicopter and a dive team, more than three hours to find her. She was pronounced dead at the scene."She's gone," Cherubin said, tears welling beneath her glasses Monday afternoon. "And it hurts. It hurts so bad."The Hillsborough County Medical Examiner's Office performed an autopsy Sunday. According to that report, Arriyanna died beneath 5 feet of water in an accidental drowning.The would-be adoptive mother at 11159 Golden Silence Drive, where Saturday's party was held, declined to comment Monday. But Cherubin said the woman "loved that little girl with her whole heart."Arriyanna had been in the woman's care before, according to Hillsborough Kids Inc.'s records. She was Arriyanna's foster mother when the girl was a newborn in July 2001."(Arriyanna) began her life with her, and she ended her life with her," Cherubin said. "It's heartbreaking."Cherubin said she took care of Arriyanna for about a year. She has four other special needs foster children in her home, all boys. Arriyanna was her "beautiful little girl."Every day, Cherubin would dress her, brush her hair in front of the mirror, walk her to the bus, hum along to the child's ever-changing song."She was so full of life," Cherubin said. "Everybody she meets falls in love with her."Though the autism hampered her ability to use words, Arriyanna was a vocal child. She mimicked noises and gestures to communicate what she wanted."I knew all her sounds," Cherubin said. "I knew which were her footsteps coming down the hall. She was only quiet when she went to sleep."Cherubin said she was not at the birthday party on Saturday when the girl disappeared. When she got the frantic call from the adoptive mother, Cherubin said she thought Arriyanna may have wandered off to take a nap; that's why no one could hear her singing.Neither Cherubin nor the prospective adoptive family has faced disciplinary action in the past, according to Department of Children and Families records. Hillsborough Kids Inc. lauded the would-be adoptive family as one of the agency's most dedicated and well-trained medical foster families.But even the most well-cared-for children can fall through the cracks. Throughout the investigation, several agencies have misreported Arriyanna's age and the spelling of her name. Records maintained by the state differed from a birth certificate, which differed from the Medical Examiner's report, which differed from the case worker's report kept by Cherubin.This, officials said, is likely due to human error.As DCF continues to investigate the circumstances surrounding the drowning, Hillsborough Kids is working with both foster families to provide crisis and grief counseling."Right now, we're focused on caring for the families and ensuring their wellbeing," said Hillsborough Kids spokeswoman Jeanine Bedell. The organization also will handle funeral arrangements. It will be a private service, open only to Arriyanna's family and friends.Times researcher John Martin contributed to this report. Marissa Lang can be reached at [email protected] or (813) 226-3386.