Mubin Shaikh says he's haunted by a video image: A 3-year-old boy uses a large knife given to him by his parents to cut off his teddy bear's head.

Shaikh is a Canadian Muslim who was radicalized as a young man and is now an expert on countering violent extremism. He now uses that video to train police and intelligence services.

Shaikh told a U.N. Security Council meeting on children and armed conflict Tuesday that it's a "real-life story of where we are today and what we will deal with tomorrow."

He said armed groups around the world are using children to carry out attacks, build their ranks and promote their beliefs.

Shaikh urged action to prevent recruitment — and to demobilize and rehabilitate radicalized children.