The group behind a controversial atheist bus-poster campaign is urging parents not to label their children with their own religious faith.
The British Humanist Association (BHA) has launched a series of billboard advertisements in capital cities.
The posters are part of a campaign to challenge state-funded faith schools.
But a representative of the Christian Schools Trust questioned who would "fill the vacuum" if parents did not pass on their fundamental beliefs.
Professor Richard Dawkins, who has part-funded the BHA campaign in London, Edinburgh, Cardiff and Belfast, says labelling children as "religious" is a form of brainwashing.
The posters show one or two young children surrounded by religious labels, such as Catholic, Muslim and Hindu, mixed with secular descriptions including Marxist and anarchist.
The advert's slogan says: "Please don't label me. Let me grow up and choose for myself."
'Freedom'
Campaign supporters hope the posters will discourage people from assuming that children share their parents' beliefs.
Last January a £140,000 advertising campaign was launched by the BHA on buses and the London Underground with the message: "There's probably no God. Now stop worrying and enjoy your life."
Ariane Sherine, who had the idea for the bus and Tube campaign, said: "One of the issues raised again and again by donors to the campaign was the issue of children having the freedom to grow up and decide for themselves what they believe.
"I hope this poster campaign will encourage the government, media and public to see children as individuals, free to make their own choices, and accord them the liberty and respect they deserve."
The BHA said the billboards were going up to coincide with Universal Children's Day on Friday.
Graham Coyle, a teacher and national team leader at the Christian Schools Trust, which represents 43 independent schools, questioned what the BHA was asking parents to do.
"They seem to be saying that they don't want parents to pass on to their children their fundamental beliefs - about what is right and wrong, about respect for other people and living in harmony," he said.
"If that is what they are saying then they are asking parents to abrogate their responsibilities. And if parents don't pass on these beliefs who is going to fill the vacuum?
"To say that we are labelling our children by passing on our fundamental values is mistaken."
He added: "If a humanist says to his child 'I don't believe in God' then he is making a statement and passing on that belief."