Children are eating half of their daily recommended intake of sugar before they arrive at school, according to research from Public Health England (PHE).
A survey of 200 parents with children aged four to 10 found that children in England consume more than 11g of sugar at breakfast alone. It also found they have eaten more than three times the recommended amount of sugar by the end of the day.
The study, taken from the annual National Diet and Nutrition Survey, discovered that the majority of parents (eight out of 10) thought their children's breakfast was healthy.
PHE has launched an app, as part of its new Change4Life campaign, in a bid to combat health problems linked to sugar intake. The Be Food Smart app enables parents to scan barcodes to see how much sugar, salt and saturated fat is contained in food products.
Alison Tedstone, chief nutritionist at PHE, said: "Children have far too much sugar, and a lot of it is before their first lesson of the day.
"It's crucial for children to have a healthy breakfast, but we know the mornings in a busy household can be fraught. That's why we've developed our Be Food Smart app, taking some of the pressure off parents and helping them to choose healthier food and drink options for their children."
Sara Stanner, science director at the British Nutrition Foundation, added: "When analysing a number of breakfasts from families across England, we were concerned to see the high amount of free sugars and low amount of fibre in many of these.
"We know a healthy breakfast can make an important contribution to children's vitamin and mineral intakes and its consumption has been linked to many positive health outcomes. There are plenty of healthier options available so we need campaigns like Change4Life to help busy parents make the right choices for their families."
More than one in five children start primary school overweight or obese, rising to more than a third by the time they leave.
The recommended daily maximum is no more than five cubes of sugar for four to six year olds and no more than six cubes for seven to 10 year olds per day.
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