McCready defied her visitation rights with 5-year-old son Zander last week by taking him from his father's home without permission.
US Marshals later found McCready and Zander at the home of the country singer's boyfriend in Arkansas and took the child to a foster care facility.
The 'Guys Do It All the Time' star is currently attempting to regain legal custody of Zander from her mother Gayle Inge, who has cared for the boy for the last four years.
In a preview of her 20/20 interview aired on Good Morning America on Friday (December 9), McCready accused Inge of physically abusing Zander and exposing him to extreme religious groups.
"Zander was being beaten with a wooden spoon. There are scars on Zander's back. There are scars on his bottom and his legs from the spoon," she alleged in the interview.
McCready continued: "My mother believes that she is a prophet sent from God… They were encouraging my son to go around with them to churches and stand up on stage and, you know, scream gibberish, and then everyone [would] act like it was something amazing that he said."
On her decision to protect Zander at all costs, McCready said: "I couldn't imagine loving something so much that instead of wanting to just lay down and die, I wanted to stand up and fight."
Her mother Inge has denied all allegations of abuse.
McCready will return to court for another custody hearing next week.
In the midst of the custody battle, McCready has announced that she is five months pregnant with twins.
McCready's full interview airs tonight (December 9) on 20/20 at 10/9c on ABC.
Watch a preview of Mindy McCready's 20/20 interview below: