WOBURN — After insisting for almost three years that her 13-month-old son died of an acci­dent, Christina Hancock pleaded guilty Thursday to ­involuntary manslaughter, bringing an end to the case and allowing Hancock to avoid prosecution on a charge of first-degree murder.

Hancock was sentenced to eight to 10 years in prison by Middlesex Superior Court Judge Maureen Hogan, agreeing to the sentence recommended by prosecutors.