Children in the UK exceed the maximum recommended sugar intake for an 18-year-old by the time they are 10, according to experts.
This is based on their total sugar consumption from the age of two, says Public Health England (PHE).
Children consume much more than they should, around eight excess sugar cubes a day or 2,800 excess cubes per year.
PHE wants families to cut back to help tackle obesity, tooth decay and other illnesses linked to excess sugar.
But UK children are consuming around 52g or 13 cubes of sugar a day, says PHE, based on results from the National Diet and Nutrition Survey.
Half of the sugar in children's diets comes from sugary drinks, sweets, biscuits, cakes, puddings, sugary breakfast cereals and higher-sugar yoghurts and puddings.
Making such swaps every day could remove around 2,500 sugar cubes per year from a child's diet, but swapping chocolate, puddings, sweets, cakes and pastries for healthier options such as malt loaf, sugar-free jellies, lower-sugar custards and rice puddings would reduce their intake even more, according to the Change4Life campaign website.
Dr Alison Tedstone, chief nutritionist at PHE, said: "Children are consuming too much sugar, but parents can take action now to prevent this building up over the years."
PHE is working with the food industry to cut 20% of sugar from the foods children consume most by 2020.
In May 2018, PHE published progress against the first-year sugar reduction ambition of 5%, which showed an average 2% reduction in sugar across categories for retailers and manufacturers.
While breakfast cereals and yoghurts and fromage frais were among the categories meeting or exceeding the 5% ambition, some products in these categories are still high in sugar.
Consumers should check the labels on packaging to judge if products are high or low in sugar.