WOONSOCKET — The attorney general will seek to try a 17-year-old boy accused of beating and raping a 2-year-old girl Sunday as an adult.

The baby’s mother, 24, had left her teenage boyfriend watching over her toddler and her three-month-old son at an apartment near Bourdon Boulevard while she went to a nearby apartment Sunday afternoon.

The teen has been charged with first-degree sexual assault by means of forcible rape and first-degree child abuse. The police say he allegedly bit, beat and raped the 2-year-old. The three-month-old baby was apparently unhurt.

Michael Healey, the spokesman for the attorney general, said that state law requires his office to file a petition for a waiver of juvenile status for 17-year-olds accused of rape, child molestation or murder.

“Obviously given the heinousness of the allegations, Attorney General [Patrick] Lynch thinks this respondent should be held and has instructed our prosecutor to file a waiver petition,” Healey said.

On Monday, the teenager is scheduled for a probable cause hearing in Family Court to determine if there is probable cause to hold him, or if none exists, to release him to his family. The prosecutor will petition Family Court Chief Judge Jeremiah Jeremiah to allow the state to try the teen as an adult and waive him out of Family Court to Superior Court, Healey said.

“Given the facts supporting this allegation, even if the law didn’t specify that we seek the mandatory waiver, Attorney General Lynch would seek a discretionary waiver anyway because the facts … are beyond revolting,” Healey said.

The baby’s mother called the police after she noticed red marks and bruises on her toddler and her boyfriend’s explanations of what had happened did not make sense to her.

During questioning of the teenager, the police who originally set out to investigate whether he had physically abused the toddler, determined that he had also allegedly sexually assaulted her. The child was taken to Landmark Medical Center and then to Hasbro Children’s Hospital, where she was held for 72 hours for observation. Doctors found bruises and bite marks on the child’s body, as well as evidence that she had been sexually assaulted, according to the police.

Mike Burk, assistant to the director of state Department of Children, Youth and Family said that the agency has launched an investigation into the allegations as is customary. The agency has about 10 days to make its determinations and take the appropriate actions, he said.

Burk said the children are in the custody of their mother. He said that the toddler was discharged from the hospital on Wednesday.

The teenager, whose name is not being released because he is a juvenile, is being held at the Rhode Island Training School pending the probable cause hearing Monday.

tpina@projo.com