Editor's note: Tune in Christmas Eve and Christmas Day to catch the final re-airings of this year's CNN Heroes tribute show. "CNN Heroes: An All-Star Tribute" will air at 6 p.m. ET on December 24 and 4 p.m. ET on December 25.
(CNN) -- Jessica Rees was diagnosed with a brain tumor at age 11, and she and her parents would drive to the hospital every day to receive outpatient treatment.
"One day we were leaving, and she just simply asked us, 'When do all the other kids come home?'" said her father, Erik.
When Jessica found out that many of them would have to stay at the hospital, she wanted to help "make them happier, because I know they're going through a lot, too," she said.
So she started making JoyJars -- containers full of toys, stickers, crayons, anything that might brighten a child's day.
"She was really particular about what would go in the jars," said her mother, Stacey. "It had to be something cool, it couldn't be cheap or flimsy."
Jessica created 3,000 JoyJars before she passed away this January. But her parents are carrying on her legacy.
By the end of 2012, more than 50,000 JoyJars will have been delivered to young cancer patients through the Jessie Rees Foundation.
"It's what she started, and it's what we'll continue to do," Stacey Rees said.
Jessica was one of three "Young Wonders" honored this year at "CNN Heroes: An All-Star Tribute."
"What makes Jessie a Young Wonder is that she cared," her dad said. "And in the midst of a world that says focus on yourself, it's all about you, she said, 'No, it's not.' "
When Will Lourcey was 6 years old, he asked his parents why a man was holding up a sign that said, "Need a meal."
His parents explained homelessness and hunger to him, and Will felt compelled to do something about it. Soon, he came up with FROGs -- Friends Reaching Our Goals -- an organization in which he and his friends find fun ways to raise money to fight hunger.
From running a lemonade stand to having businesses sponsor kids in sporting events, Will has raised more than $20,000 for his local food bank in Texas and, in turn, provided more than 75,000 meals to people in need.
"When you see somebody who gets so engaged and gets so much of the community engaged, it's an endorsement of the battle that we fight to end hunger," said food bank director Bo Soderbergh.
In his quest to spread awareness for his cause, Will has spoken before the Fort Worth City Council, worked with the former mayor of Fort Worth and written for the White House blog.
But Will is not resting on his laurels: He has his sights set on not only eradicating hunger in his hometown, but throughout Texas, the United States and the world.
Cassandra Lin is changing the world one french fry at a time.
Four years ago, at the age of 10, she decided she wanted to do something for the environment and help the less fortunate in her Rhode Island community. She gathered her friends and created Project TGIF -- Turning Grease Into Fuel. The organization collects used cooking oil from restaurants and homes, refines it and then distributes a percentage of it to families who can't afford to heat their homes.
So far, Cassandra and her team have collected 130,000 gallons of used cooking oil and donated $81,000 for the purchase of biofuel. This has amounted to 21,000 gallons of BioHeat distributed to 210 homes. These efforts have also offset 2 million pounds of carbon dioxide emissions from the environment.
Last year, the group helped draft legislation that makes it mandatory for all businesses in Rhode Island to recycle their used cooking oil. The bill went into effect January 1.
"I was trying to talk about biodiesel and just could not get anywhere with it," said Caswell Cooke, a town councilor in Westerly, Rhode Island. "And (Cassandra) came along and did it, to get restaurants to recycle their grease. ... The fact that it was coming from kids made it hit home a lot harder. 'The child shall lead them' sort of thing."
Cassandra's next goal is for the program to be implemented throughout New England.