Shocking posters featuring the gristle, bone and connective tissue found in fast food such as burgers and chicken nuggets are being put up around the country to make children think more about what they eat.

The campaign, by the British Heart Foundation, aims to get children to think more about what is in their food and improve their diet. The full gory reality of what some fast food manufacturers put in their products is censored in the posters, but children can see the full images on the charity's website.

Research carried out for the foundation reveals the reality of young people's knowledge of food: more than one in three eight- to 14-year-olds do not know chips are made from potatoes. In a survey of 1,000 children, one in 10 thought chips were made mainly of oil, while others suggested eggs, flour and even apples. The 36% in the dark about chips were matched by 37% who failed to identify cheese's origins in milk.

There was some comfort in the survey's findings. Seven in 10 children know the recommended number of fruit and vegetable portions each day is five, although younger children were more clued up than older ones.

The BHF is pressing for an end to the marketing of unhealthy products to children, the provision of affordable and appealing nutritious alternatives and more opportunities for children to learn how to cook. Celebrities such as the sports presenter Gaby Logan, the bands Sugababes and Girls Aloud, the actor Fay Ripley and the cricketer Andrew Flintoff are all backing the campaign.

The BHF chairman, Peter Hollins, said: "Banning foods or telling children not to eat them is not enough. We must engage children in understanding why certain foods are less healthy than others and encourage them to become interested in what's on their plate."