McCready, whose once-bright career has been overshadowed in recent years by her legal woes and drug addiction, has visitation rights with her son Zander, but her parents have physical custody of him.
People.com said McCready picked the child up from her father's Cape Coral, Fla., house Tuesday, then took off with him.
A Florida judge has ordered the onetime "Celebrity Rehab" star to bring the boy home by 5 p.m. Thursday, People.com reported.
"My son is not missing," McCready said via Twitter late Tuesday. "Police established that this afternoon via Skype. I have been fighting the Florida court system to protect my son, and bring him home. Please do not worry."
Celebrity Families of 2014 [PHOTOS]
Gwen Stefani finishing new solo album in Miami