A third of seven- to 10-year-old girls believe that they are judged on their appearance and a quarter feel the need to be perfect, according to a study by Girlguiding UK.

The charity’s annual girls’ attitudes survey, published on Tuesday, found that girls were suffering from a crisis in body confidence, with 61% of those aged seven to 21 feeling happy with how they look, down from 73% in 2011.

The study – the largest annual research of its kind – suggests that girls as young as seven feel under pressure to be pretty.

More than a third (35%) of seven- to 10 year-old girls agreed that women were rated more on their appearance than their abilities, and 36% said they were made to feel their looks were their most important attribute.

Campaigners said the findings showed the need to combat the “objectification and harassment … ruining girls’ lives”.

The survey also revealed low levels of body confidence among girls. Almost two-fifths (38%) of the same age group think they are not pretty enough, while a similar number feel they are judged more on their appearance than their ability. Almost a quarter (23%) said they felt they needed to be perfect, while 15% said they felt embarrassed or ashamed by the way they looked.

The majority of seven- to 10-year-olds said that what would most improve their lives would be if people would stop judging girls and women on the way they look.

The survey questioned 1,627 girls and young women aged between seven and 21 about a range of issues from health and wellbeing to relationships and careers.

Sam Smethers, chief executive of the Fawcett Society, said women and girls were “persistently judged on what they look like” and suffered “significantly higher” rates of depressions and mental illness. “This is serious. As a society we need to face up to the fact that objectification and harassment is ruining girls’ lives and we are letting it happen,” she said.

Dr Carole Easton, chief executive of the Young Women’s Trust, said the survey revealed the presence of “gender inequality” from a young age. “If we are serious about ensuring that everyone has an equal opportunity to get on in life, then much more must be done to ensure a level playing field – starting from childhood and into young adulthood, not least by challenging gender stereotypes,” she said.

Becky Hewitt, Girlguiding director said: “This year’s girls’ attitudes survey demonstrates the shocking impact that focusing on girls’ appearance is having on the youngest girls in society.”

“Girls have told us to stop judging them on how they look. Every day in guiding, girls inspire us with their bravery, sense of adventure and their kindness. We are calling on everyone to show girls that they are valued for who they are – not what they look like.”

Lyra, 10, a Brownie from south London, said: “I think more girls are judged on their appearance than boys. I don’t think it’s fair that men get treated differently to women. You have to treat everyone the same.”

Liddy Buswell, 18, Girlguiding advocate and Brownie leader, said she was shocked but not surprised by the findings. “I’ve experienced these issues first-hand. I’ve witnessed girls unwilling to speak to groups because of how they look, I’ve heard girls saying they’ve been called names at school and aren’t confident trying new activities as a result.

“No girl should have to worry about the way she looks – she should be having fun and enjoying herself. This year’s survey is a damning indication that something needs to be done to tackle this growing issue.”

Girlguiding UK launched its first “body confidence” badge in 2014 in response to what it described as a crisis in how girls perceive themselves. It is now launching a new social media campaign to make the public think about how they compliment or praise girls, asking them to praise young women for their achievements or attributes, rather than the way they look, using the hashtag #YouAreAmazing.

Anne Longfield, the children’s commissioner for England, said: “Children I speak to tell me they sometimes feel enormous pressure to behave and look a certain way. It’s disturbing that so many young girls think their appearance is the most important thing about them and large numbers feel they have to be perfect. Concerns about body shape can spiral out of control into eating disorders or mental health problems without the right support.

“Girls, and increasingly boys, are bombarded with images in the media and the 24/7 availability of social media can put additional pressure on children. It can be really helpful if parents are able to discuss and challenge unhealthy attitudes children may have and don’t ignore warning signs. Schools also have a huge role to play in building resilience to the negative pressures and attitudes girls may face, and lessons that do this need to be a priority in all school timetables.”