- Nine-year-old schoolgirl Niamh Clarke-Williams officially opens Olympic Stadium
- Joins Seb Coe on stage to press button and release 1,000 white balloons into sky
- Followed variety show hosted by TV presenters Gabby Logan and Vernon Kay
- More than 40,000 spectators watched ceremony and test events in final Games rehearsal
When it comes to Olympic ceremonies, London is keen to make sure its schoolchildren play a starring role.
Nine-year-old Niamh Clarke-Willis became the latest youngster to take center stage when she pressed the button for the official opening of the Olympic Stadium on Saturday.
The wet weather didn't stop more than 40,000 people attending the ceremony, dubbed "2012 Hours to Go," at the Olympic Park in east London.
Local schoolgirl Niamh was picked to take part in the historic event after Paralympic archer Danielle Brown fired arrows into a spinning target, covered with the names of 100 children in the crowd.
She joined London 2012 chairman Sebastian Coe on stage to press the giant blue button, releasing 1,000 white balloons into the stormy sky.
Niamh followed in the footsteps of nine-year-old Tayyiba Dudhwala, who played a starring role in the Beijing to London handover ceremony in 2008.
Millions around the world watched as Tayyiba handed David Beckham a football which he kicked into the crowd from atop a double-decker bus at the closing ceremony.
Four years on and London has again turned to its children, with plans to also feature hundreds of pupils in the opening ceremony, directed by Oscar-winning "Slumdog Millionaire" filmmaker Danny Boyle.
The official opening of the stadium followed a variety show hosted by British TV presenters Gabby Logan and Vernon Kay. Celebrities and athletes took part in a series of stunts, games and competitions, including a bicycle relay challenge and "zorbing," where people roll around inside giant transparent plastic balls
Two of Britain's most celebrated Olympians, rower Steve Redgrave and swimmer Mark Foster, were among those present to mark the venue's official opening.
Spectators also watched about 90 minutes of an athletics championship for British university students, a test event held at the stadium.
Coe, a two-time Olympic gold medalist in the 1980s, said it was an important milestone with the Games now less than three months away.
"The whole purpose of the test is to go away, sit down, review what we understand and make sure that it's even better when it's finally tested at the Olympic grounds," he told CNN.
There were reported queues as spectators arriving at the four entrances to the Olympic Park passed through airport-style security, with metal detectors and bag scanners in operation.
Police helicopters kept watch over the grounds while officers carrying guns patrolled the site.
However, visitors appeared cautiously positive about the stadium facilities, with one family telling CNN the seating was comfortable but there was a lack of rubbish bins.
The stadium will host the four opening and closing ceremonies for the Olympic and Paralympic Games, as well as the track and field events.
With waterways on three sides, spectators will access the 80,000-capacity stadium via five bridges.
The structure was built using 10,000 tons of steel, considerably less than for other Olympic stadiums, the organizers say, and with an emphasis on sustainability.