A documentary on evangelising young people entitled "Jesus Camp" will launch this weekend, featuring kids praying and worshipping at Bible camps and youth events in the US.

Pastor Becky Fischer's Bible camp in North Dakota, US, "Kids on Fire," was among the groups who participated in the film.

"I want to see them as radically laying down their lives for the gospel as they are in Palestine, Pakistan and all those different places," Fischer said. "Because, excuse me, we have the truth."

"A lot of people die for God," one camper said, "and they're not afraid."

"We're kinda being trained to be warriors," said another, "only in a funner way."

The film has caused a split among evangelicals. Some say it's designed to demonise, while others have embraced it, including Fischer, who's helping promote the film.

"I never felt at any point that I was exploited," Fischer said.

"I think there is a push right now in a lot of evangelical churches to definitely keep the teenagers and keep the children in the faith," said Heidi Ewing, co-director of "Jesus Camp." "And this is one version of that attempt."

This camp is, by many accounts, a small - and perhaps extreme - slice of what some say is a growing, intensifying evangelical youth movement.

Over the past decade and a half, enrolment at Christian colleges is up 70 per cent in the US. Sales of Christian music in the US are up 300 per cent. Tens of thousands of youth pastors have been trained.

It is young people who are targeted through Christian music festivals, skateboard competitions and rodeos.

"This is an enormous youth movement," said Lauren Sandler, a secular, liberal feminist from New York City who spent months among the believers researching her new book, "Righteous".

Sandler says the evangelical youth movement will have a negative impact on the country's future, because even the most moderate young evangelicals are inflexible on issues such as abortion and gay marriage.

"It's an absolute, straight-up us-against-them," Sandler said. "It's, you're either with us or you're against us. ... Not only are you a sinner, but you are working for the enemy - the enemy being Satan."