A Massachusetts mother and her boyfriend are accused of killing the woman's 4-year-old daughter.

The mother, Lymari Acevedo, and her boyfriend, Richard Castillo, pleaded not guilty Friday to charges with assault and battery upon a child causing substantial bodily injury and wantonly permitting substantial bodily injury on a child. The have been ordered held without bail.

Worcester authorities tell the Boston Herald that the couple blamed the child's death and injuries on her being "clumsy."

Court records state that the little girl's back had a "clearly visible bruise that appears to be the hand print of an adult."

Castillo told authorities that the hand print occurred when he "whacked" her back to try to get her breathing again, according to the Herald.

The boyfriend also told authorities that Acevedo was the only one who would discipline the girl and that a family doctor raised the question about abuse to him several months ago.

The mother told authorities that she did grab the girl's arm when she wouldn't listen, according to the paper. She also claims she approached Castillo about her daughter's injuries.

Police say they found the girl unresponsive at the couple's home at about 5:45 p.m. on Thursday. She was taken to the hospital where she was pronounced dead.

Police say emergency responders as well as hospital medical staff saw signs of possible physical abuse.

An autopsy has been scheduled to determine a cause of death.

A 6-month-old child in the home has been placed in state custody.

The Associated Press contributed to this report.