Grace Callwood receives her award from host Nick Cannon at the 2016 Nickelodeon HALO Awards, which air Sunday. Callwood started a nonprofit for needy kids after she was diagnosed with cancer. (Craig Barritt/Getty Images for Nickelodeon)

When Grace Callwood was 7, she was diagnosed with non-Hodgkin’s lymphoma, a type of cancer. She had to miss school and take a break from her favorite hobby, dance, because her body became too weak.

Still, she found that she had enough strength to volunteer.

When she realized she couldn’t fit into her new back-to-school clothes because her cancer treatments caused her to gain weight, she donated the clothes to two girls who had lost all of their possessions in a fire.

“It gave me a good feeling,” she told KidsPost recently, “so I kept going.”

To help a hospital and a foundation for sick children, she started a lemonade stand, raising $633 in four hours. And then she decided to start a charitable group of her own: the We Cancerve Movement, a nonprofit organization that donates clothes, food and care packages to homeless, sick and foster children. In four years, the organization has helped more than 3,700 kids in and around her home town of Abingdon, Maryland.

Shreya Papneja, 13, and her brother Shivam, of Herndon, hand out healthful snacks to preschoolers at a local Montessori school last year. (Rajiv Papneja)

Grace, 12, is now cancer-free. She was one of four kids honored at this year’s Nickelodeon HALO Awards, a concert special that airs Sunday and celebrates kids who are “helping and leading others.” She’s one of many kids who are trying to better their communities.

“You don’t always have to do something huge,” she said, encouraging kids to find ways to volunteer. “Just do what you can.”

Shreya Papneja, 13, started her own charitable organization after a cardiologist, or heart doctor, told her that more than one-third of kids and teens are overweight or obese. She started doing her own research and, using her programming skills, created a website to spread the word about the importance of exercise and healthful eating.

Through the Children’s Health Awareness Program in Schools, or CHAPS, she now leads presentations and nutrition workshops at schools around her home town of Herndon.

“A lot of organizations out there, it’s usually an adult or an elder telling younger children” to change their habits, she told KidsPost. “But they don’t really connect as well and don’t know what children are doing right now.”

Shreya said she changed her own snacking habits as a result of her research and now eats apple slices instead of chips. “I know how hard it is to make a change,” she said.

Alyssa Mathew, 14, is trying to make a different kind of change. Two years ago, her interest in science led her to get involved in a gardening program at her school. But instead of growing apples or tomatoes, she’s growing oysters — and doing it to help the Chesapeake Bay.

Ellicott City, Maryland, students, from left, Eleanor Karueh, Grace Fioretto and Alyssa Mathew check on their oysters with parent Sabrina Fioretto. (Tiffany Friend)

“One adult oyster can filter 50 gallons of water in a day,” she explained. That helps to keep the bay’s water clean. Oysters also provide shelter for fish and other animals.

Alyssa and about 70 of her classmates at Dunloggin Middle School in Ellicott City, Maryland, are helping to bring back the bay’s oyster population, which in the past 200 years has been hurt by overharvesting, pollution and disease.

Last month, under the watch of science teachers Dan Blue and Pam Kidwell, Alyssa and other students spent about three hours checking water conditions and counting baby oysters on Kent Island, where the oysters are growing in cages alongside a dock.

She’ll return later this spring to check and clean the cages, and then to move more than 9,000 adult oysters to a protected area in the middle of the bay.

“It’s kind of a good feeling,” she said, “to know that we’ve raised these oysters and are making a difference in the water.”