Where You've Seen Them Before: The Young Stars On "It's Okay To Not Be Okay"

Moon Woo-Jin

The young Moon Gang-tae is portrayed by 11-year-old Moon Woo-jin. At his age, he’s already had more than 20 titles under his name. Prior to IOTNBO, he also appeared in the K-Drama “The King: Eternal Monarch” as the young version of Kim Kyung-nam’s character, Kang Hyun-min. This adorable child star has been grabbing viewers' attention not only for his good looks but also for his huge potential as an actor. It was in 2006 when he first made his TV debut via MBC’s “Person Who Gives Me Happiness.”

Photo Credit: @wj_2009

Moon Woo-jin also portrayed the young versions of the characters of the following actors: Yang Se-jong in "My Country: The New Age," Jang Dong-gun in "Arthdal Chronicles," Seo Kang-joon in "Watcher," Jang Ko-yong in "Kill It" and "Come and Hug Me," Kim Nam-gil in "The Fiery Priest" and "Live Up to Your Name," Seo Do-young in "Kangnam Scandal," Cha Eun-woo in "My ID is Gangnam Beauty," Park Seo-joon in "What's Wrong With Secretary Kim," Lee Sang-yoon in "About Time," Kim Kang-woo in "My Contracted Husband, Mr. Oh," Park Jin-woo in "Man Who Sets the Table," Im Si-wan in "The King in Love," and Kim Ji-hoon in "Bad Thief, Good Thief."

Photo Credit: @wj_2009

The other K-Dramas he appeared in are "Once Again," "Vagabond," "The Beauty Inside," "Life on Mars," and "Oh, The Mysterious."

Photo Credit: @wj_2009

Kim Soo-In

11-year-old Kim Soo-in is the child star behind the young version of Seo Ye-ji's Ko Mun-yeong character. Just as Seo Ye-ji impresses viewers with her take on the mysterious character, Kim Soo-in is also gaining praise for her steely portrayal. She made her debut back in 2016 via a cameo in "Weightlifting Fairy Kim Bok-Joo."

Photo Credit: @09suin

The other Korean actresses whose young characters she portrayed in K-Dramas include: Park Joo-hyun in "A Piece of Your Mind," Sooyoung in "Tell Me What You Saw," Shin Ye-eun in "He is Psychometric," and Uee in "My Only One."

Photo Credit: @09suin

The young Kim Soo-in also had stints in the following K-Dramas: "The Player," "About Time," "Dal-Soon's Spring,""20th Century Boy and Girl," "While You Were Sleeping," and "Stranger." Last year, she also starred in a KBS Drama Special titled "A Child Saw."

Photo Credit: @09suin

Lee Kyu-Sung

The actor who portrayed the young version of Oh Jung-se's Moon Sang-tae character is 28-year-old Lee Kyu-sung.

Photo Credit: @lee.kyu.sung

A newbie in the Korean entertainment industry, he only debuted in 2017, appearing in a few episodes of K-Drama "Prison Playbook." The year that followed, he was given roles in TV series "Sketch" and movie "Swing Kids."

Photo Credit: @lee.kyu.sung

If you were impressed by his acting in IOTNBO, you have to see "When the Camellia Blooms," too! As Park Heung-sik, he plays a supporting yet integral role in the award-winning rom-com thriller. If his role here is any indication of what projects he could potentially excel in, then he might just evolve to become as versatile as actor Oh Jung-se who also happens to be his co-star in "When the Camellia Blooms."

Photo Credit: @lee.kyu.sung

Park Seo-Kyung

Park Seo-kyung was born on October 18, 2009. She appeared in IOTNBO as the young Nam Ju-ri (Park Kyu-young).

Photo Credit: @09suin

If she looks familiar to you, then perhaps you've also seen her portray the young version of actress Park Min-young in the recently-concluded K-Drama "When the Weather is Fine." She also appeared as the young version of Choi Moon-kyoung in the series "Children of Nobody."

Photo Credit: @seokyung3136

She also appeared in K-Dramas "Secret Boutique" and "Possessed."

Photo Credit: @seokyung3136

Here are BTS snaps on the set of IOTNBO from the Instagram accounts of these young stars...