Every child born on Monday will be given the chance to play a part in the 2012 Olympics if London wins the right to host the event.
An average of 1,855 babies are born each day in December.
As part of a "2012 day" to promote the bid, the children will be offered roles in the opening and closing ceremonies.
Bid chairman Sebastian Coe said it was a once-in-a-lifetime opportunity.
London is competing against Paris, Madrid, New York and Moscow to host the games and a final decision will be made on 6 July.
Monday was chosen as 2012 day - because it is the 20th day of the 12th month.
"To mark 2012 Day we wanted to do something special which benefits the whole country and provides a legacy," he said.
"We are all looking to the future with great anticipation and the most important part of the future is our children.
"The Olympics is a once-in-a-lifetime opportunity for us all and this can make it extra special for the children and families who get involved."
An average of 1,855 babies are born each day in December in the UK.
If the London bid is successful, it would be the first time in 60 years that the Olympic Games has been held in the UK.
Parents can register their children at:
Or you can write to: London 2012, The Pink Centre, 2a Tinworth Street, London, SE11 5EJ.