AOL.com : Yoko Ono, Hugh Jackman help launch UNICEF's latest campaign (by Emily Cegielski)

UNICEF celebrated the 25th anniversary of the Convention on the Rights of the Child with a concert, featuring performers from around the world, at the UN General Assembly on Thursday. Yoko Ono, Hugh Jackman, Steve Harvey and a slew of other celebrities were on hand for the musical celebration and to help launch the organization's new #IMAGINE campaign.

"Twenty-five years ago the Convention on the Rights of the Child asked us all to imagine a better world for children and, not only to imagine it, but to make that vision real," UNICEF Executive Director Anthony Lake explained. "And today, we celebrate the wonderful progress that has been achieved, but we also need to recall all the millions of children that we have not reached."

#IMAGINE is how UNICEF hopes to reach those kids that have been left behind.

Using the John Lennon classic as an anthem, the organization has challenged people across the globe to record their own version of the song using a newly-released smartphone app. These individual recordings, along with those from well-known singers, will then be produced by David Guetta into one multilingual, 'world' version of 'Imagine.'

UNICEF is calling it the 'largest ever global sing-along,' and plans to release the song with an interactive music video in the lead-up to New Year's Eve.

The initiative promises to have a lot of participation from celebrities. Seth Green, Katy Perry and Lorde all made appearances in a video shown at Wednesday's event, and Hugh Jackman and Steve Harvey waxed poetically about the campaign in front of attendees.

"All children everywhere have the same rights -- no matter where they or what they believe," Jackman remarked before bringing Yoko Ono on stage. Ono, who gave UNICEF the rights to use Lennon's song, seemed thrilled with the collaboration. Saying that the future was now, she urged everyone to "seek peace, act peace and spread peace."

Speaking with AOL.com before the concert, Harvey pondered, "What would happen if the word 'imagine' was erased? What if there was no imagination? Albert Einstein said once that imagination is a preview to life's coming attractions. So, if there is no 'imagine,' then where are we at?"

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