Singer Rachel Stevens, rowing hero Sir Steve Redgrave and CBBC's own Angellica Bell and Jake Humphrey were among the stars supporting Sport Relief.
They want kids and adults across the country to join them in taking part in a one-mile sponsored run on 10 July.
It costs £1 for under 16s to register, with races being held across the UK.
Runners get one red sock when they register, and another after they have crossed the finish line.
They can choose between taking part in a time trial, or just running for fun.
Sport Relief was launched in 2002, when a whopping
£14.4 million was raised.
Sir Steve said: "The money is already helping young people across the country who are forced to live tough lives, as well as people in the world's poorest countries."
TV presenter Tess Daly urged runners: "Exercise your imagination as well as your legs. People are dreaming up weird and wonderful ways of going the extra mile."
Olympic athlete Colin Jackson seemed a bit nervous about the run.
"As a sprint hurdler, a mile seems a very long way. It might take me a bit longer than some of the others," he joked.