Targets to cut 20% of sugar from nine popular children's foods will not be enough to ensure youngsters are adhering to their maximum recommended daily intake, health officials have admitted.
New guidelines from Public Health England (PHE) set out how the food industry can reduce the amount of sugar children consume through everyday foods - including reducing chocolate bar sizes and cutting the amount of sugar in many popular products.
But even if the nine categories of food all reduced sugar levels by 20% by 2020, youngsters would still be exceeding their recommended daily allowance, PHE said.
The foods at the centre of PHE's sugar reduction project are the top nine categories of products providing sugar in children's diets - yet they account for less than half of children's total sugar intake.
The guidelines say sugar can be reduced through reformulating products, reducing portion sizes or helping consumers shift to low or no added sugar alternatives.
Childhood obesity is an "urgent problem", PHE said
The Government's Childhood Obesity Plan called for a 20% reduction of sugar in the nine food categories by 2020.
PHE said the new guidance will help the industry achieve this.
It is hoped that this measure, along with the Government's sugar levy on soft drinks, will lead to a 20% reduction in the number of children who are overweight over the next decade.
PHE claimed that if the sugar reduction targets are achieved, around 200,000 tonnes of sugar could be removed from UK diets each year by 2020.
The new guidelines set out recommended sugar and calorie limits in the nine categories - breakfast cereals, yoghurts, biscuits, cakes, puddings, ice creams and lollies, chocolate confectionery, sweets and morning goods such as croissants and crumpets.
They also set out limits for jam, chocolate spread and peanut butter.
Asked whether the 20% reduction would mean children would generally stop routinely exceeding their recommended daily allowance, Alison Tedstone, chief nutritionist at PHE, said: "It doesn't take you all the way, there is a way further to go.
"There is still a way to go because sugar is still coming from other products. Pasta sauces, for example, often have sugar in."
PHE's report sets out how each food category might reduce sugar, suggesting that cakes could reformulate recipes or reduce portion sizes while chocolate bars and sweets could reduce portion sizes.
"We know that customers tell us in our surveys that they want smaller portion sizes, we know that reducing portion sizes supports health," Ms Tedstone said.
"We are all human - if we are given that portion we will eat it despite us knowing it is too big so it's going with the grain of health."
PHE chief executive Duncan Selbie said the agency is not ordering manufacturers to make chocolate bars smaller, but was suggesting this was a "legitimate way" to achieve a reduction in sugar.
Asked about the benefits of a voluntary sugar reduction programme over regulation, Ms Tedstone said: "We think that if we were to develop regulation for a reformulation programme at the moment, it would tie us up in knots for a long time and we have an urgent crisis with childhood obesity."
Mr Selbie said: "The scale of our ambition to reduce sugar is unrivalled anywhere in the world, which means the UK food industry has a unique opportunity to innovate and show the rest of the world how it can be done.
"I believe reducing sugar in the nation's diet will be good for health and ultimately good for UK food business.
"We can't duck the fact a third of children are leaving primary school overweight or obese and obesity generally is having a profound effect, not just on the costs for the health service, but on the overall health of the nation."
Public health minister Nicola Blackwood said: "This Government believes in taking a common sense approach to improving public health and that includes changing the addictive relationship our children have with sugar."
PHE set out a raft of other steps including looking at sugar consumed when eating out - often seen as a treat even though people are eating out more - and examining baby-weaning products, some of which have "very high" levels of sugar.