Elsa from Frozen and Belle from Beauty and the Beast joined Spiderman on a visit to the city centre hospital on Monday (April 9).
They sang Let it Go and Beauty and the Beast and played games with the children during an hour-long party.
The visit from Leeds children's entertainment company Parties for my Princess was organised through Leeds Cares, the charity partner of Leeds Teachings Hospitals.
Parties for My Princess director Hayley Johnson, 31, of Horsforth, sad: "The children were happy to see us. They were absolutely over the moon, smiling and singing along. It was magical to see the childen's faces.
"We love our job so much because we get to make children happy and we were very excited to be able to give some of the poorly children a very special experience that they will never forget."
Kevin Gerrie, interim director of fundraising at Leeds Cares, said: "The visit from Parties for my Princess was a wonderful gift for young patients on the ward - everyone had a magical morning."
"The generosity of people like Hayley helps us to enhance the healthcare environment and enables Leeds Children’s Hospital to deliver the best outcomes for children and young people."
Miss Johnson, who worked as a singer on cruise ships for four years, said she launched Parties for My Princess just over a year ago.
She said: "We truly believe we are the second best thing to Disney. For those children not as fortunate, or not able to go to Disneyland, we bring their favourite Princesses and superheros to them."
"We invest a lot of money in our costumes and wigs which all come from America and we always stay in character."
Miss Johnson said the idea of gifting a visit to Leeds Children's Hospital came about after she ran a competition to win a free party on the Parties for my Princess Facebook page.
Miss Johnson said one woman who entered the competition said she would like to donate the prize to Leeds Children's Hospital if she won.
It prompted Miss Johnson to contact the hospital later and offer a free party for children being treated there.