Sgt. D.B. Grant of the King County Sheriff's Office said authorities were able to track the pair - Mason J.J. Bennatts-Miller, 6, and his mother, Sandra Bennatts, 34 - to the Stevens Pass area Monday morning by pinging the mother's cell phone.
Snohomish County sheriff's deputies then spotted a grey 2009 Acura RDX with Washington state license plate number 787-YZO that was believed to be the vehicle they were in as it headed east on Highway 2 near Skykomish.
As deputies followed the vehicle, it accelerated to dangerously high speeds of up to 100 mph and deputies broke off the pursuit.
Eventually the mother stopped the car in the Stevens Pass area and was trying to flag down other vehicles when authorities caught up with her and took her into custody without incident. The boy was found safe inside her car.
"At that time we were finally able to get her," Grant said. "We're very happy it ended up this way."
The boy, Mason Jonathan Joseph Bennatts-Miller, was abducted from his grandmother's home at 39723 186th Place SE in Auburn on Sunday night.
Authorities say his mother, who does not have custody of him, forced entry into the grandmother's home at knifepoint at about 8 p.m. Sunday. She then assaulted the grandmother, tied her up and took her son after ransacking the house. She may also have taken a handgun.
The little boy's grandmother was finally able to untie herself several hours later and alerted authorities about the abduction.
The little boy, who is autistic, has blond hair and brown eyes, stands about 3 feet tall and weighs about 50 pounds.
A King County Sheriff's Office spokesperson says the boy's mother has attempted to take him back on previous occasions.