Holly Cota, 28, and boyfriend Scott Edwards, 33, were arrested last Friday in connection with injuring the child, WTHI-TV reported.
The boy was taken to the Union Hospital in Terre Haute, the New York Post reported, citing the Tribune Star.
Edwards is facing charges of aggravated battery and neglect of a dependent. Officers said Cota lied about how the child's injuries occurred, the station reported.
The emergency room staff told WTHI that the boy also suffered bruises and other injuries in addition to the split tongue.
"I am appalled. I am disgusted. My heart hurts. When that's all you can think about is that poor baby going through that with nobody for him to be his voice and say stop...you're hurting me. It just breaks my heart," Chelsie Loose, a family friend, told the station.