Half the sugar consumed by children comes from unhealthy snacks and sugary drinks, according to a campaign that suggests parents look out for snacks of no more than 100 calories at a time.
Public Health England (PHE) warned that on average, children are consuming at least three unhealthy snacks and sugary drinks a day, with around a third consuming four or more.
This means that children can easily consume three times more sugar than is recommended.
Its new Change4Life campaign encourages parents to "Look for 100 calorie snacks, 2 a day max," to help them offer healthier snacks in a bid to tackle what it's called an "epidemic" in which a third of children leave primary school overweight or obese.
Half of children's sugar intake, currently around seven sugar cubes a day, comes from unhealthy snacks and sugary drinks, leading to obesity and dental decay, PHE says.
This is while 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.
Meanwhile, each year children are consuming almost 400 biscuits, more than 120 cakes, buns and pastries, around 100 portions of sweets and nearly 70 of both chocolate bars and ice creams - washed down with more than 150 juice drink pouches and cans of fizzy drink.
The campaign, which is the first Change4Life to promote healthier snacks, will offer parents special offers on a range of healthier snacks, including fruit and vegetables at selected supermarkets.
Healthier suggestions for snacks and drinks while at home and on-the-go include fresh or tinned fruit salad, chopped vegetables and lower fat hummus, plain rice cakes, crackers, malt loaf, crumpets and Scotch pancakes.
PHE says its new advice applies to all snacks apart from fruit and vegetables, as children should still be encouraged to eat a variety of these to achieve their five a day.
"The true extent of children's snacking habits is greater than the odd biscuit or chocolate bar. Children are having unhealthy snacks throughout the day and parents have told us they're concerned," Dr Alison Tedstone, chief nutritionist at PHE, said.
"You see children buying chips coming out of school and buying a bag of chips on their way home from school, and that's part of the reason why we have an obesity epidemic in this country.
"To make it easier for busy families, we've developed a simple rule of thumb to help them move towards healthier snacking - look for 100 calories snacks, two a day max."
Dr Tedstone added that with an average ice cream containing around 175 calories, a packet of crisps around 190 calories, and a pastry around 270 calories, the amount eaten throughout the day by children and adults alike can add up.
Justine Roberts, chief executive and founder of Mumsnet, says the volume of sugar kids are getting from snacks and sugary drinks alone is "mind blowing".
"It can often be difficult to distinguish which snacks are healthy and which aren't," she said.
"This rule of thumb from Change4Life will help parents make healthier choices, which can only be a good thing."
PHE is working with the food industry to cut 20 per cent of sugar from the products children consume most by 2020.
