More than one in 10 children in Scotland have started primary school overweight or obese since 2005, a study by Cancer Research UK shows.
It said almost 83,000 four to five-year-olds entered P1 carrying excess weight between 2005-2006 and 2014-2015.
The charity warned obesity could become a "crippling burden on society and the NHS" if action was not taken.
The Scottish government said it encouraged people to be more active, eat less and eat better.
According to Cancer Research UK's Statistical Information Team, four and five-year-olds in Scotland are also "more likely" to be overweight than in other areas of the UK.
Cancer Research UK, which carried out the study to mark World Obesity Day, said excess weight could be linked to 13 types of cancer.
Launching its "Scale Down Cancer" campaign, the charity called on the Scottish government to do more to tackle obesity by restricting billboard advertising of unhealthy food and drink and reducing supermarket multi-buy discounts.
Prof Linda Bauld, Cancer Research UK's cancer prevention expert, based at the University of Stirling, said: "We should be concerned about the picture this paints for the health of the nation as we know that obese children are around five times more likely to become obese adults.
"Obesity is also linked to 13 types of cancer including bowel, breast and pancreatic. If left unchecked, we run the risk of obesity becoming a crippling burden on society and the NHS.
"The Scottish government must do more to serve up a better future for our children and protect youngsters from being bombarded by junk food marketing on TV, as well as the barrage of supermarket multi-buy offers on sugar and fat-laden food and drinks."
The charity's study indicated that over the past decade, about 15% of children in P1 each year were overweight or obese.
The nation also has one of the heaviest populations in Europe with two in three adults overweight or obese, researchers said.
The cost of obesity to the NHS in Scotland is estimated to be £600m a year.
Case study - Kirsty Thomasson: "Dump the junk"
Nurse and mother-of-three Kirsty Thomasson, who weighed 13st and was a size 18 before slimming down, is backing the campaign.
She decided to lose weight after her trousers burst at the seams, and is now 9st 4lb and a size eight.
The nurse, from Inverurie in Aberdeenshire, said she now had more energy for her children.
She said: "I think advertising does influence what you buy, that's why the junk food companies invest in it.
"If I saw a poster for a sugary snack, or an advert on TV, then it would definitely have encouraged me to put a particular biscuit or a fizzy drink in my shopping basket - especially if it was part of a 'buy one get one free' offer.
Ms Thomasson added: "I think it's awful that so many children now are obese and it's about time we all took responsibility and did something about it."
Scotland's Minister for Public Health Aileen Campbell said: "We have consistently called on the UK government to ban junk food advertising before the 9pm watershed and we are looking at what further effective actions we can take within the powers available to us, including the use of multi-buy promotions, as well as examining a range of actions to improve diet, physical activity and education.
"We are engaging with the food and drink industry on action to offer healthier choices, rebalance promotions, and reformulate products, with a focus on reducing calories, salt, fats and added sugar."
Geoff Ogle, chief executive, of Food Standards Scotland said: "FSS fully supports the Scottish government call for junk food advertising to children to be prohibited prior to the 9pm watershed.
"Our preference would be for a UK-wide approach because it makes it easier for consumers, industry and government to work together to take action."
He said the FSS had recommended a package of measures to Scottish ministers earlier this year including fiscal measures and regulation around food and drink promotions.
This included a recommendation to reduce portion sizes and to introduce tougher targets for reformulation of foods and drinks.
The Scottish Conservatives health spokesman, Donald Cameron, said the SNP had shown no "clear ideas" about how to tackle obesity.
"The Scottish government needs to outline in detail exactly what it intends to do to help parents keep their children's weight down," he said.
"They won't want to see tokenistic gestures, but hard and fast solutions which encourage a more active lifestyle and healthier diet."
Scottish Labour said it was a "sad reality" of Scotland that people from a poorer background were more likely to be in poorer health.
The party's health spokesman Anas Sarwar said: "We need to tackle the root causes of inequality in our communities and that starts with an end to austerity and stopping the cuts to vital public services that impact most on the poorest and most vulnerable in our society."