22 year old Grace , of Christian and Nigerian descent left her London home in 2012 to enter into an arranged marriage and live in Syria with her husband.
Mr Dare told Channel 4 News he had reported her to the police on three occasions before she left for Syria, telling them:
"She's behaving in a very funny way". "They told me she's free," he added. "They said she's above 18."
The horror clip ends with a child thought to be from the UK hailing the deaths, saying: "We will kill the Kuffar (unbelievers) over there".
Now, Sunday Dare, 59, is begging Grace, known as 'Khadijah', to bring the boy home.
Mr Dare told the Sun:
"Grace, Grace, come home with my grandchildren. "Come home, we love you, come and face the music. You caused it yourself, you've got to face the music."
In a video unearthed by The Mirror in 2014, burka-clad Dare fired an AK-47 rifle and pleaded with fellow Brits to fight by her side in Syria.
A security source said at the time:
"The threat Dare poses is immense. "Her notoriety has evolved so rapidly that she has achieved a celebrity like status among jihadists fighting in Syria and those who are thinking of travelling abroad to join IS."
"The threat from homegrown would-be terrorists such as her is very great. Dare has now become a top priority."On her Twitter account - which has since been taken down - Dare posted pictures of her four-year-old son holding a machine gun.
The boy would be roughly the same age and shares similar features to the child wearing military fatigues and an ISIS bandana in the new video.