The average child will have exceeded the recommended sugar intake for an 18-year-old by their 10th birthday, according to research by Public Health England (PHE).
The heath body has said that while sugar intakes have fallen in recent years, the average child still consumes the equivalent of 2,800 excess sugar cubes each year.
A third of children leave primary school either overweight or obese and PHE are working with the food industry to remove 20% of sugar from products most contributing to children's sugar intakes by 2020.
Parents are also being advised on ways to reduce sugar consumption, including switching from sugary drinks and cereals.
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.