The video shows five boys standing in front of five men in orange jumpsuits and the boy captioned as Abu Abdullah al-Britani (the Briton) is white, The Press Association reported.
A child captioned Abu al-Bara al-Tunisi (the Tunisian) addresses the men - apparently Kurdish fighters - promising more violence, according to the BBC.
The other children are said to be Abu Ishaq al-Masri (the Egyptian), Abu Fu’ad al-Kurdi (the Kurd) and Yusuf al-Uzbaki (the Uzbek).
The identity of the child said to be British has not been verified.
Children have featured prominently in IS propaganda.
In February, IS released a video purportedly showing a young British boy - thought to be four-year-old Isa Dare - blowing up a car and killing three prisoners inside.
He is the the son of Muslim extremist Grace “Khadija” Dare from Lewisham, south-east London, who travelled to Syria in 2012.