Mo Farah on a mission to inspire a generation to get off the couch

Double gold medallist calls for more sports facilities and is shocked by fall in UK life expectancy

Mo Farah has a mission. He wants to find a way of finishing what he began over the course of two unforgettably raucous Saturday evenings in east London. Seven weeks later here he is sitting in a damp gym in south London, a starkly urban setting on a dour autumn morning; next door Boris Johnson is gallivanting with a group of schoolchildren.

Children have been the "other" moment for Farah from this mother and father of all sporting summers; his twins, Amani and Aisha, are now five weeks old.

Farah is here to highlight a report into tumbling levels of activity among children – it concludes that the generation among which the twins will grow up can expect to live up to five years less than their parents.

"As a parent it touches you," says Farah. "The video [shown to launch the report] said five years and that's what really got me. That is a strong message. I have twin daughters who are five weeks old and five years... you don't want to imagine them losing five years. It's quite shocking."

The "L" word is now the watchword post-London 2012: legacy. There is ample evidence, not only from this report, produced by the Young Foundation, that sport participation among young people has declined. Figures earlier this year from Sport England showed a drop in the number of people aged 16-25 playing sport since London was awarded the Olympics, a Games secured with the readily repeated promise to inspire a generation.

Farah has done one part of that through his once-in-a-generation double gold. Now he wants to help get bums off seats; he feels a responsibility.

"For sure," he says. "We won't achieve things overnight but we can do something about it, and if we get more parents involved we can do something about it. The government need to help make it happen. I would like to see more funds in the grass roots. Kids need facilities.

"Life has changed a lot, life moves faster, people don't have a lot of time with their kids after being at work and if we could have the funding for volunteers to go to clubs. There were a lot of volunteers at London who genuinely wanted to help out."

Farah will soon return to his US base – once visas and passports for the twins are sorted – to close an extraordinary stay in his home country. "I didn't realise so many people had watched it. When I am in a restaurant [people] do the 'Mobot' on my head. I say, 'just let me eat my food'," he says and then laughs at the absurdity of it all.

Once back in Portland with his coach Alberto Salazar, they will lay out a plan for next season and beyond. Next year brings the world championships and after that a likely switch to marathon running, with the 2014 London race a possible debut.

First though, there is an appetite for more on the track, to dominate his distances as the great Kenenisa Bekele did for eight years ahead of Farah's emergence. "I believe I can – that's what great athletes do and that's what I intend to do," says Farah. "I am thinking about the track for the world championships but in the back of my mind I will know when I am going to do a marathon. I would like it to be London. As a kid I did the mini-marathon so it would be rude not to do the full thing."

Mo Farah was at Lilian Baylis Old School to announce the findings of Move It, a report, written by the Young Foundation and funded by Nike, which warns that England faces an epidemic of physical inactivity. For more information, visit designedtomove.org