Five-year-old boys who display chivalry towards girls are sexist as they see women as weak and helpless, a study has concluded.

Playing princes and princesses at school might be just an innocent game, but could also be a sign of "benevolent sexism" among boys who believe girls need "rescuing", according to psychologists at New York University.

Patronising and undermining behaviour towards women can then persist into adult life, the researchers claim.

Dr Andrei Cimpian, who led the study, published in the journal Sex Roles, said: "It might seem cute when a boy acts in chivalrous ways toward girls, or when a girl pretends to be a princess who's waiting for a prince to rescue her.

"Many times, this is just play, with no deeper meaning. But other times, these behaviours - even though they may seem inoffensive - might signal that children view women in a negative light, as weak, incompetent, and unable to survive or thrive without a man's help."

Dr Cimpian believes early exposure to sexism in childhood could contribute to this.

"Boys may be less likely to recognise that their benevolent attitudes toward women are, in fact, patronising," he said.

"They may hold on to the belief that men ought to protect women because this view is in line with social norms and may be reinforced throughout their upbringing."

The researchers studied the attitudes of more than 200 children aged between five and 11 in New York City and Urbana-Champaign in Illinois.

They were asked if a series of statements, including some which exhibited "benevolent sexism", such as 'men need to protect women from danger', were right or wrong.

Their analysis showed that "benevolent sexism" persisted among boys as they grew up but declined for girls.

Ros McNeil, assistant general secretary of the National Education Union, told The Telegraph that sexism is inbuilt in young boys.

"Young children begin to grow into sexism rather than out of it and it's important we challenge those stereotypes - secondary education is too late," she said.

"We can't think 'boys will be boys and they'll grow out of it'. These stereotypes are daft for everybody. We don't want to limit boys' ability to show their emotions.

"Before children start talking they are listening and watching what adults do, what colour clothes they put on and who does what around the house. Because we can't see it, we don't see how those stereotypes are being formed.

"They are invisible and hard to spot but we know they're there because when we ask primary students about men and women they say men are stronger and women are better at working on beauty counters and multitasking."

Martin Daubney, co-founder of the Men & Boys Coalition, told The Telegraph that claiming chivalry is sexist is "contemptible and damaging".

He added: "This study is not only ludicrous and divisive, but it’s methodology is bogus. Feeding leading questions to five-year-olds is about as scientific as tea leaf reading.

"Social scientists like this peddle the poisonous myth that we live in a world where children are secretly sexist and racist. Thankfully, theirs is a world that no decent human wants any part of."