While en route, Jerrod Wall spoke with his older child on the phone, who informed him that said the accused and Jenna Wall were in the house and he had heard gunshots.
The children heard the gunfire, but didn't see the fatal encounter that left their mother dead, police said.
Their 63-year-old grandmother, Elizabeth Wall, had taken the boys outside Thursday in Georgia and put them in a truck, according to Cobb County Police Sgt. Dana Pierce.
Then, Wall "goes right back inside, and shoots and kills their mom," Pierce told The Post.
Police say Wall fatally shot her 35-year-old daughter-in-law, Jenna, who was reportedly in the midst of divorcing Wall's son.
The timeline of events is still being determined, Pierce said.
But at some point on Thursday, Wall called her son, who showed up at the Powder Spring, Georgia, home "within moments" of the shooting.
"She is inside the house still with the weapon, and at some point in a conversation between him and his mother, she puts the weapon down," Pierce said. "And then he calls police; he calls 911 at that point."
Wall was taken into custody on charges of felony murder, aggravated assault, possession of a weapon during the commission of a felony, and third-degree cruelty to children, Cobb County police said in a news release.
She was being held without bond, online jail records indicate. It is unclear if she already has an attorney.
The shooting happened in the home of Jenna Wall's parents, according to Pierce.
They were not home at the time of the incident.
The Atlanta Journal-Constitution, citing an arrest warrant, reported that Elizabeth Wall's son, Jerrod, was at work when he received a telephone call from his mother, who reportedly told him to come collect the children.
That call left Jerrod Wall so concerned "about what just transpired in the conversation, or what he was told in the conversation" - that he left work and went to the house, Pierce said.
"While en route, Jerrod Wall spoke with his older child on the phone, who informed him that said the accused and Jenna Wall were in the house and he had heard gunshots," the warrant stated, according to the newspaper.
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The Journal-Constitution reports:
When Jerrod Wall arrived at the Wyndham Woods Drive home, off Antioch Road, his estranged wife was dead and his mother was pointing a handgun at her head, police said.
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Jenna Wall taught kindergarten at a local elementary school, according to the school's website.
In a blog post, she wrote that her sons were "the most precious gifts from God," and that she was "truly honored and proud to be their mom."
© 2016 The Washington Post
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)