It's frightening that one in four Australian children is overweight, says former Olympic champion Cathy Freeman, and she counts herself lucky to have grown up a healthy and active kid.

Speaking at the launch of the Global Children's Challenge, Ms Freeman said she was fortunate to have had an active upbringing and a health conscious mother. She told reporters, Mum grew up on an island where she ate a lot of fruit, fresh fish from the ocean and turtles.

I was brought with very strict instructions in terms of diet, I was very fortunate.

Fifty thousand primary school children will be given a pedometer each, by the Global Children's Challenge, to check their progress on a web site. According to Ms Freeman, the program will encourage children to walk 15,000 steps a day, which will take just over an hour.

Herb Elliot, 72, another former Olympic champion said he enjoyed walking and aimed for about 10,000 steps per day. I spent 40 years jogging to keep fit and two metal hips came out of all that running, said Mr Elliot at the launch.

He said walking is the most fantastic way of keeping yourself healthy. Another participant, Darcy Burgess, from Bronte Primary School in East Sydney said he had taken 12,561 steps by mid-Wednesday and kept active by joining in sports. He said, I do soccer and go to the beach.

Roman Giuffre, also from Bronte Primary School said he had recorded 13,365 steps on his pedometer by mid-day and that his mother helped him lead a healthy lifestyle. He said, I'm playing football at the moment and soccer and I love to surf.

I eat well as my mum gives me good lunch and does good home-cooked meals.

Twenty five per cent of children of five and 17 were overweight or obese in 2007-08, four percentage more than from the levels in 1995, according to the Australian Bureau of Statistics.

If weight gain continues on its current path, by 2020, a third of Australian children will be overweight or obese. Australian children today are ranked as one of the most inactive of all in developed countries, based on a number of studies.

If these habits go uncontrolled well into adulthood, the risks for premature death, and other health consequences such as type II diabetes, heart disease, osteoarthritis and some cancers will increase.