DENVER -- A 31-year-old homeless mother will be sentenced Thursday after pleading guilty to having sex with the teenage son of a family who took her in.

Tani Leigh Firkins was charged in Jefferson County, but not in Denver, even though the boy's family said numerous sexual assaults took place in both counties. Firkins even gave birth to a child after getting pregnant during one of the sexual encounters.

The boy's parents ran a day-care center where Firkins worked five years ago. The 14-year-old victim had been hanging out at the center when the relationship began, according to Firkins' arrest affidavit.

Social services removed the infant and two other children of Firkins shortly after the baby was born in 2004 and just before her arrest.

The Jefferson County District Attorney's Office originally filed 12 felony counts against Firkins, but 11 of them were dropped as part of her plea bargain. Charges of contributing to the delinquency of a minor, marijuana sale and distribution, and sex assault on a child were thrown out when Firkins admitted felony sexual exploitation of a child on June 13.

The family is not being identified in order to protect the identity of the victim.

The boy's father told 7News that the sex assaults covered a three-year period, starting when his son was 14. Now 19, the boy is helping his family care for his newborn son.

The father said he is frustrated because even though more than half of the assaults occurred in Denver, the Denver district attorney has not filed charges against Firkins.

District Attorney Mitch Morrissey will meet with boy and his father on Sept. 6. "As far as I'm concerned, the investigation in Denver is not closed," he said.

The father said Firkins assaulted his son between 50 and 100 times and he's worried that she'll only end up with a 12-year sentence, based on her guilty plea in Jefferson County.