Officers from 37 local authorities analysed the nutritional content of 279 samples of food and drink consumed daily by children, including fizzy drinks, breakfast cereals, crisps, ready meals and pizzas.
It was calculated the maximum level of salt that could be consumed in a day was 13.8g, twice the recommended daily amount for an 11-15 year old.
The Trading Standards Institute presented the results at a meeting of the All Party Parliamentary Group for Consumer Affairs and Trading Standards at the House of Commons last week.
Phil Thomas, lead officer for the TSI, said the existing labelling system made it hard for consumers to work out the salt content of foods.
"Manufacturers only have to say how much sodium is in food. To work out how much salt there is, a consumer has to make a calculation. Most consumers spend fewer than ten seconds selecting food. You can't expect them to make a calculation about whether a food is high in salt before they buy it. We need a quick and easy way for consumers to make these choices."