The song is Pie Jesu...Merciful Jesus, it was written for the children who died in the Oklahoma City bombing.
3rd to eleventh graders from Penndel will sing it during Saturday's 9/11 Mass of Remembrance, in New York City.
Katie Cleary's memories of the historic and tragic morning come from stories of her dad, an Air Force pilot, and what he was asked to do, after the terrorist planes struck the World Trade Center:
Katie, a 5th grader at Our Lord of Grace School said, " My dad was flying right around our house and around Philadelphia and near New York.
Your dad was protecting the skies over and New York on that fateful day?. "Yes, " responded Katie.
One of only a few boys in the school choir, Seamus Smiley also has a relative who experienced the horror of September 11th.
Seamus, also a 5th grader says, "My aunt was in the Pentagon. The plane hit her office, but she was getting a cup of coffee, so she survived."
His younger sister wasn't even born on that tragic morning.
3rd grader Tessa Smiley said, "I just feel very sorry for the people who experience this disaster, and who lost people that they loved."
" I was here in school that day. It was difficult because we had a lot of parents, who worked in New York. There was anxiety and worry that they were safe," said, Cathy Galia, music teacher at Our Lord of Grace.
Most of these children are so young; the post 9/11 world is all they've known.
Morgan Bailey, a 4th grader says, "When I heard about it from my mom and dad I started to cry and tear up."
"I didn't even know what it was, I had no idea," added, 11th grader, Daniele Walter.
Some remember the fear on their parents faces, and sensed the seriousness of what was happening.
Galie said, "I experienced 9/11, and this will be their 9/11 experience, to go, and see many faces of people who have been touched by what happened."