My, how she's grown!

Shortly after Teen Mom 2 star Leah Simms' 13-month-old daughter, Aliannah, underwent an emotional MRI procedure, the tot seems to be taking a step in the right direction.

On Tuesday's all-new episode of the MTV series, the little girl's parents celebrate a new milestone. But it doesn't come without a price.

As the above preview clip shows, Leah, 18, and her husband, Corey, 20, make a friendly $5 wager as to if their daughter can roll over from her belly to her back.

"You won daddy five bucks," Corey tells his "show baby" after she demonstrates her moves. Mom Leah, meanwhile, is happy to fork over the funds. "That's one bet I'm happy to lose," she says.

Corey is dedicated to helping his daughter live a full life as the family determines what, if any, physical limitations she may have.

"I told Leah that no matter what Ali has, no matter what is wrong, she'll live a very active life," Corey tells "As long as I'm able to get her out there, she'll be able to do it. Whatever she wants."

Teen Mom 2 airs Tuesday at 10 p.m. (EST) on MTV.

By Allison Corneau for For more Channel Surfing, click here.