U.S. Marshalls said they later found the country singer and the boy hiding in a closet, which McCready denies.
McCready said she would "not ever think that me taking my own child, that I carried for nine months, that I gave birth to in the hospital by myself would ever be breaking the law."
"What I did was to protect my child, and there's not a person in the world that's going to tell me that that is wrong," she said.
McCready, who is pregnant with twins, said her son was anguished when, she said, U.S. Marshalls came to get the boy with a SWAT team-like force last Friday.
"He was screaming, 'Please don't touch me, please don't touch me, please don't touch my mommy. Please, leave me alone, I want to be with my mommy,' " McCready remembered.
An official with the U.S. Marshalls said that authorities used standard operating procedure when taking Zander into custody and had a social worker with them.
"There was no forced entry made. No battering ram," said David Rahbany, Chief Deputy U.S. Marshall for the Eastern District of Arkansas.
McCready's mother, Gayle Inge, is Zander's guardian. McCready has alleged that her son faced physical and emotional danger at Inge's Florida home, a claim Inge has denied. The two have been engaged in a custody battle over Zander for years.
McCready said she grew so desperate that, during a visit to the Cape Coral, Fla. home of her father - Zander's grandfather, who shares custody with the grandmother although they are divorced - she took her son and left.
"I know there are rules that are written down that we're supposed to follow, and guidelines that we're supposed to follow, but there's a difference between right and wrong, and right and wrong in my opinion should come first, always," McCready said.
Inge was appointed Zander's guardian in 2007 while McCready served six months in prison for a probation violation related to an earlier drug charge.
McCready said she was pleased with a juvenile court judge's custody ruling this week. Details of the ruling have been sealed. Zander is currently in foster care.
Watch more with McCready on "Good Morning America" tomorrow and watch the full interview on "20/20? at 10 p.m. ET.