The two children chosen to front Richard Dawkins’s latest assault on God could not look more free of the misery he associates with religious baggage. With the slogan “Please don’t label me. Let me grow up and choose for myself”, the youngsters with broad grins seem to be the perfect advertisement for the new atheism being promoted by Professor Dawkins and the British Humanist Association.

Except that they are about as far from atheism as it is possible to be. The Times can reveal that Charlotte, 8, and Ollie, 7, are from one of the country’s most devout Christian families.

Their father, Brad Mason, is something of a celebrity within evangelical circles as the drummer for the popular Christian musician Noel Richards. Now a web designer and photographer, Mr Mason has been supplementing his income for years by providing photographs to agencies who sell them on to newspapers and advertising campaigns.

He said: “It is quite funny, because obviously they were searching for images of children that looked happy and free. They happened to choose children who are Christian. It is ironic. The humanists obviously did not know the background of these children.”

He said that the children’s Christianity had shone through. “Obviously there is something in their faces which is different. So they judged that they were happy and free without knowing that they are Christians. That is quite a compliment. I reckon it shows we have brought up our children in a good way and that they are happy.”

Gerald Coates, the leader of the Pioneer network of churches, which Mr Mason and his family used to attend before they moved to Dorset, said: “I think it is hilarious that the happy and liberated children on the atheist poster are in fact Christian.”

The British Humanist Association said that it did not matter whether the children were Christians. “That’s one of the points of our campaign,” said Andrew Copson, the association’s education director. “People who criticise us for saying that children raised in religious families won’t be happy, or that no child should have any contact with religion, should take the time to read the adverts.

“The message is that the labelling of children by their parents’ religion fails to respect the rights of the child and their autonomy. We are saying that religions and philosophies — and ‘humanist’ is one of the labels we use on our poster — should not be foisted on or assumed of young children.”

The images of the children were sourced from istockphoto.com, on which photographers upload images for sale to designers, in return receiving a portion of each download fee.

Those who have welcomed the campaign include the magician and illusionist Derren Brown and the author Philip Pullman, who said: “It is absolutely right that we shouldn’t label children until they are old enough to decide for themselves.”