Opposition leaders have written a joint letter to the Prime Minister urging her to tackle the obesity crisis.
The cross-party letter comes as TV chef Jamie Oliver is campaigning for a ban on advertising unhealthy foods prior to the 9pm watershed.
In the letter to Theresa May, opposition leaders say that taking no action would result in the current generation of children living shorter lives than their parents.
Jeremy Corbyn, Nicola Sturgeon, Sir Vince Cable, Caroline Lucas and Jonathan Bartley urge Ms May to "take bold action to tackle one of the greatest health challenges of our time".
They call for 13 measures, including an end to buy-one-get-one free junk food deals.
Dozens of Labour MPs and peers are to gather in Westminster on Wednesday as part of Oliver's £AdEnough campaign.
In a post on his website, Oliver writes: "It's time we put child health first. I'm calling for the government to introduce a 9pm watershed on junk food advertising on TV, and for proper controls on what ads kids see online, in the street and on public transport.
"Crucially, this campaign isn't about stopping big brands from advertising full stop; it's about making sure kids aren't being targeted with unhealthy products. It's about controlling the time and place."
He adds: "If kids are constantly being targeted with cheap, easily accessible, unhealthy junk food, just think how hard it must be to make better, healthier choices. We have to make it easier for children to make good decisions.
"These ads undermine any positive work we're doing in schools or at home to tackle the rise of childhood obesity. Currently, there's nothing in place to protect our kids from seeing these adverts - apart from literally covering their eyes! And that's where our £AdEnough campaign comes in."