People are recommended to eat five pieces of fruit and vegetables a day
One in three parents say their children know more about healthy eating campaigns than they do, a poll shows.
And most told the Department of Health survey that rising food prices put five portions of fruit and vegetables a day out of their reach.
The survey of 1,000 parents in England also revealed three-quarters of them were unaware that frozen and canned varieties counted towards the total.
Food experts said school campaigns were improving children's knowledge.
The five-a-day figure is recommended to people across the UK, but research suggests that only just over half of the population eat this amount
There is evidence that sticking to a five-a-day diet can reduce the risk of cancer, heart disease and stroke.
School campaigns mean that many children are aware of what they can and cannot eat, but the surveyed suggests that many parents are not.
One mother, Debbie Hussey, told the survey that she had to be told by her daughter to swap baked potato for broccoli to reach the target.
Half of those polled did not know that vegetables in cooked food - such as a can of tomatoes in spaghetti bolognese - also counted towards the total.
Others wrongly thought that baked potatoes could be one of the five, or mistakenly discounted dried, or even fresh fruit.
Potatoes and other starchy foods do not count towards the recommended target.
While children often knew more, half of those surveyed tricked their parents into thinking they had consumed a full portion after eating only a tiny amount of things they did not like.
However, health minister Dawn Primarolo said the survey provided evidence that health teaching in schools and elsewhere was reaching children.
"We welcome the fact that children are absorbing our five-a-day messages and can teach their parents - and peers - to eat more healthily too."
Azmina Govindji, from the British Dietetic Association, said that getting children involved in shopping or cooking made them more likely to eat healthier food.
She added: "If healthy eating messages can get through to children, then they have a lot of power in the home, and can ask their parents for the kind of food they need to be eating."