Christa B. Allen as Young Jenna
13 Going on 30 was Allen's first major film role, and she's been quite busy ever since. In 2009, Allen played the younger version of Jennifer Garner's character again in Ghosts of Girlfriends Past. However, Allen is most known for her role as Charlotte Grayson on Revenge, which has been on since 2011. You can keep up with Allen on both Twitter and Instagram.
Sean Marquette as Young Matt
Marquette's done voice work, lending his voice to both Sam Dullard on Rocket Power and Mac on Foster's Home for Imaginary Friends. In 2014, Marquette co-starred in the Civil War drama Field of Lost Shoes, opposite Jason Isaacs and David Arquette. His most recent acting credit is Sundown, which comes out later this year. You can follow Marquette on both Twitter and Instagram.
Alexandra Kyle as Young Tom-Tom
Kyle co-starred in the 1996 thriller Eye for an Eye, opposite Sally Field and Kiefer Sutherland. Soon after, she worked with Sutherland again in A Time to Kill, based on the famous John Grisham novel. Since 13 Going on 30, she's had recurring roles on Without a Trace, Days of Our Lives, and Justified. In 2011, she worked on A Thin Line and Disconnected. You can follow Kyle on both Twitter and Instagram.
Alex Black as Young Chris Grandy
After playing teenage heartthrob Young Chris Grandy, Black guest-starred on CSI: Miami and ER. However, he's probably best known for playing the dim-witted jock Seth Powers on Nickelodeon's tween show Ned's Declassified School Survival Guide. Black's last acting role was in the Hallmark TV movie Generation Gap, opposite Ed Asner.
Renee Olstead as Becky
Olstead is probably best known for her TV work on both Still Standing and The Secret Life of the American Teenager. She's also an accomplished musician, and has released several albums. She recently starred in the horror-thriller Unfriended. Olstead is also heavily involved in social media — you can follow her on Facebook, Twitter, and Instagram.