Some window cleaners in Chicago have jumped on a trend and dressed up as superheroes.

According to the Huffington Post, the Chicago superheroes dressed up while cleaning windows at Lurie Children’s Hospital.

The Chicago Tribune reports that three Lurie window washers donned superhero costumes — Captain America, Spider-Man and Batman — on Tuesday in an effort to cheer up and surprise the young patients at Lurie while they went about their work. Nurses call the new tradition, which started last year, “Superhero Day.”

No one is sure where the window-cleaners-as-superheroes trend started, but it’s a great thing to put a smile on a child’s face.

While Lurie neuro-oncologist Dr. Stewart Goldman told the Tribune he has no scientific research to back it up, he feels the “Superhero Day” event and the positive feelings it inspires can help the hospital’s young patients heal.

“There is power in laughter and joy and excitement,” Goldman said.