Yoko Ono joined an international cast of musicians and other artists on Thursday at the United Nations to kick off a project using one of John Lennon's best-known songs to highlight the plight of children denied rights.

The song, "Imagine," calls for the abolition of possessions, war, and, more controversially, faith in God, and was chosen as a way to mark the 25th anniversary of the adoption of the Convention of the Rights of the Child.

"Today we celebrate the wonderful progress that has been achieved over these last 25 years, but we also need to recall all the millions of children around the world that we have not reached, those for whom life is not better," Anthony Lake, UNICEF executive director, told a packed audience at the General Assembly hall. UNICEF is the U.N.'s children's agency.