London 2012: 10,000 Londoners to be cast in ceremonies
Up to 10,000 Londoners could join the cast for the opening and closing ceremonies at the 2012 Games directed by Danny Boyle, the London mayor said.
Boris Johnson said adult volunteers did not have to be dancers or singers but needed "buckets of energy".
In a U-turn, London 2012 chairman Lord Coe said children born on 20 December 2004 would be a part of Paralympic ceremonies and the torch relay.
The 2012 babies had been promised a major role in the Olympic ceremonies.
Mr Johnson and Lord Coe were speaking at BBC London's Olympic Debate.'Greatest shows'
Inviting volunteers for the showpiece events by Oscar-winning director Danny Boyle, Mr Johnson described it as an "amazing opportunity for Londoners to be right at the heart of the Games".
The chosen 10,000 will be involved in rehearsals before joining some of the biggest talents in showbusiness.
He said: "If you are brimming with enthusiasm, passion and have buckets of energy then this is the opportunity for you.
"In return you will experience something no chequebook can buy - the chance to be part of one of the greatest shows on earth."
Details of how to apply for one of the 10,000 volunteer spots will be revealed later.
London 2012 - Begin your journey here
These new positions will be in addition to 70,000 official volunteers, for which the search has already begun, and another 8,000 people who will act as London Ambassadors during the Games.
On the 2012 Children's Promise, the Olympics organisers had initially promised a "major role" for the now six-year-olds born across the country on 20 December 2004.
But a few months ago the parents of the 700 London 2012 babies were told they will be a part of only the Olympic torch relay in their local areas.
This prompted parents to launch a petition urging organisers to keep their original promise, following which London 2012 has now revised its plans.
Lord Coe said: "We will make available Paralympic opening and closing ceremonies and given that not all those children are born in London, we felt that a role in the torch relay, that will touch 95% of the population, was a much more practical way of doing it."
Michelle Harding, from Basingstoke, Hampshire, who launched the petition, said: "I don't feel like I have won but I feel like we have achieved something.
"I would still like to go to the opening ceremony with Emily in the Olympic Games but this is the compromise that has been reached and I am quite happy with it."
The Olympic Debate will be on BBC One for viewers in the London area at 19:00 BST and afterwards on the iPLayer.