Almost a quarter girls aged eight and 11 admit their worry about appearance and weight
And by Year 6 – the final year before secondary school when pupils are 10 and 11 – a third of girls say they want to lose weight.
Some 14 per cent of boys aged between eight and 11 also worry about their appearance.
Researchers said they found girls as young as six who talked of going on a diet and boys of seven and eight already wanting a six-pack.
Sadly we are not at all surprised by the results of the survey
The study of 57 schools also found an increasing use of social media and adult websites by primary pupils.
A third of Year 6 girls communicate with pals online, and 24 per cent of boys in the same year.
A third of girls surveyed said they had seen images or videos which had upset them, and 23 per cent admitted seeing online content which was 'for adults only.'
By year 6 a third of girls say they want to lose weight
Among boys, the figure is higher with 29 per cent saying they had seen adult-only pictures or video.
The survey was carried out by the Somerset Health and Wellbeing in Learning Programme.
It concluded that modern anxieties more commonly associated with teenagers are increasingly filtering down to younger children.
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Many children believe their appearance affected the way they were treated by peers
Many children believed their appearance affected the way they were treated by peers, with 15 per cent saying they were bullied because of the way they looked, and 11 per cent because of their weight.
Education consultant Chris Calland said: "Sadly we are not at all surprised by the results of the survey.
"Children today live in an image-obsessed society and are surrounded by images of perfect looking people.
"Not only are they looking at photoshopped celebrities but also the filtered pictures of their friends through social media.
"Taking selfies, analysing their own image and constantly comparing themselves to others is taking its toll on our children and we are seeing this at a younger and younger age.
"We often work in schools where girls as young as six are worried about their appearance and talking about going on a diet.
15 per cent said they were bullied because of the way they looked
"We also meet boys of seven and eight already wanting a six-pack.
"When children are anxious about how they look it can be damaging for their self esteem and long term this can be a contributing factor to depression and mental health concerns.
"We believe that we need to start early, building body confidence in primary schools so that children are more resilient to the pressures they are being exposed to at an early stage."
11 per cent were bullied because of their weight
A spokesman for anti-bullying charity Kidscape said: "This survey shows us that younger and younger children are exposed to what we may have understood as teenage concerns such as anxiety over body image, bullying and access to adult content online.
"We need to equip our children from a young age to live safe and well, encouraging positive relationships, healthy habits and helping them make sense of what they see online."