My, how fast they grow! Teen Mom star Maci Bookout posted an adorable picture of herself with her 4-year-old son, Bentley, on her Instagram page Saturday, July 6, looking happier as ever.

PHOTOS: Teen Mom cast -- where are they now?

In the sweet snapshot, the 21-year-old is seen holding Bentley, (whom she shares custody with ex Ryan Edwards, 25), while the tot has his arms wrapped tightly around the MTV star's shoulders. "Bookout cookout with my best buddy!" the Chattanooga, Tenn., native captioned the picture.

VIDEO: Maci talks about Ryan's parenting style 

Bookout, who's currently dating fellow motocrosser Taylor McKinney, proudly raved about her son to Us Weekly back in November.

"He gets gold stars every day. I'm so proud of him," she boasted of Bentley's time in preschool. "They always write comments on why they get gold stars and normally it's because he'll clean up without being asked or follows all the rules."

VIDEO: Maci shares Bentley's latest milestones

Bookout, along with Bentley and Edwards, appeared on Teen Mom from 2009 to 2012.

This article originally appeared on Maci Bookout, Teen Mom Star, Shares Adorable Picture With Son Bentley