"This is not their fault," returning trainer (and new mom) Jillian Michaels tells PEOPLE of the one in three children who, according to national studies, are overweight or obese in the U.S. "This is about an introduction to an active lifestyle and helping them feel better about themselves."
In addition to working with 15 adult contestants, Michaels – along with fellow trainers Bob Harper and Dolvett Quince – will mentor three teenagers who will train predominately at home and will not weigh in on camera.
"It is about reeducating them and working on their goals," Michaels says of working with Sanjana Chandrasekar, Lindsay Bravo and Noah Gray.
Lindsay Bravo, 13She began gaining weight after her parents' divorce and eventually quit being a cheerleader because she was bullied for her size.
"I felt girls were laughing at me because when I jumped, my stomach would go up. I felt very uncomfortable. I would turn around and laugh at what they said and then go home and eat whatever I wanted and go to my room and cry," Bravo, who one day wants to be a gymnast, tells PEOPLE. "My mom would be, like, 'What are you doing?' I would say I saw Titanic and she would say, 'Oh, okay.' I never told my parents."
Now training predominately with Quince, whom she describes as "really nice," the eighth grader is enjoying the games and exercises the teens are learning to keep active.
"I've always tried to lose weight in the past and I would always give in to the hot Cheetos or mac and cheese, but this has been really successful with everyone motivating me," the Southern California native says of beginning her Biggest Loser experience. "Now I would love if I could get in a gymnastics class and be comfortable with myself."
Noah 'Biingo' Gray, 13Born in Maryland, he began to put on weight at age 10 when his family moved to Virginia after his father accepted a new job.
"The economy hit my family really hard and we had to start moving a lot," Gray tells PEOPLE. "It really stressed me out and that caused me to eat more."
Through his Biggest Loser training, Gray is learning to trade out the "junky foods with all the sugar" that he loves for broccoli – even though he still has to mix the broccoli in with other foods he enjoys more.
"When I leave the [Biggest Loser] Ranch, I hope to be at a more fit stage,” says the eighth grader, who wants to improve his skills as a baseball pitcher. "I love baseball with all my heart and I want to be able to keep up with my friends."
Sanjana 'Sunny' Chandrasekar, 16She was born in Chennai, India, and has since moved multiple times around the globe before settling in Rochester, N.Y.
"I was always 'the new kid' and I would be really lonely a lot of the time and would turn to food as a companion and a friend," Chandrasekar tells PEOPLE. "And while I'm doing homework I might be up until 3 a.m. stressing out and start binge eating."
Chandrasekar, an aspiring singer, hopes that by leading a healthier lifestyle she will gain the confidence necessary to audition for the lead roles in school plays and musicals that she has always wanted.
"When I am on stage I am worried that people are looking at how I look rather than listening to what I have to say or sing," says the 11th grader, who is working mostly with Michaels, whom she says "treats us differently than she does the adults."
In addition to learning to ride bikes with friends rather than go out to eat or to the movies, Chandrasekar is developing a new outlook on life thanks to Michaels.
"Jillian told me that it is not really about how others perceive you but how you perceive yourself," she says. "Being able to transform my body and how I see myself on the inside is going to be really healthier for me later in life."
In addition to the teens, 15 adults will compete on teams, each led by one of the Biggest Loser trainers. "Each team of adults will be paired with one child participant who will compete with and contribute to their respective teams," according to a press release from NBC. However, the teens will not be up for elimination.