They came to celebrate National Superhero Day, an annual holiday that celebrates "everyday superheroes" like patients, families and doctors.
Some went room to room delivering gifts and games to sick kids.
"It was really fun because I have a lot of visitors but the super heroes are really energetic so it was really fun to see new people coming," 11-year-old patient Madison Serna said.
While others just popped in for a quick 'Hello', and scaled the side of the hospital building.
"It made me really happy because the past few days I haven't even gone outside and they really brought the outside to me," patient Irene Velarde said.
Hospital doctors and nurses also joined in on the fun, wearing their own superhero gear, while NICU babies sported their own miniature masks and capes.