The offices of downtown Chicago were a little empty Wednesday.

Hundreds of corporate employees ditched the desks and cubicles to provide a helping hand at the fourth annual Backpack-a-Thon.

Over 800 volunteers — representing 37 different companies — assembled in Daley Plaza on Wednesday morning to pack 50,000 backpacks to be delivered to school children who need supplies. Chicago Public Schools students head back to class Sept. 3.

Cradles to Crayons, the nonprofit organizing the event, works with 54 social service agencies to ensure the backpacks reach students who need them, Executive Director Shoshana Buchholz-Miller said.

The backpacks — bought by Cradles to Crayons using the donations from the companies — are distributed through schools, Boys and Girls Clubs and homeless shelters.

Buccholz-Miller said the number of backpacks doubled this year but the program needs to keep growing.

“Frankly, we’re going to help 50,000 kids,” Buccholz-Miller said, “but there are probably four times that who could use our services.”

One in three children in Chicago lives in poverty, said Dr. Helene Gayle, president and CEO of the Chicago Community Trust.

“In total, 15 million school-aged children in the U.S. cannot afford supplies and prepare to go back to school,” Gayle said told volunteers before the bag stuffing began.

Volunteers, each identifiable by their bright company shirts, took their spots with their co-workers at 10:30 a.m., as a horn blared and the stuffing of 50,000 backpacks began.

Within moments, music filled the air. At the other end of the plaza, tables abound with coffee, water and bananas stood ready for volunteers.

“I love all the energy being generated by the music,” said Kathleen O’Connell, 55, one of the 155 volunteers from Bank of America.

Large wheeled carts, filled with completed backpacks, rolled from volunteer stations to moving trucks on Clark Street.

Comcast employee Amy Winchell, 51, was participating in the Backpack-a-Thon for a second year in a row.

“It’s a feeling that you can all make a difference together,” Winchell said, waiting in line with her cart. “And when you’re volunteering with co-workers, it just feels sweeter.”