Farrah Abraham, Sophia Farrah Abraham, Sophia

They grow up so fast!

Ranking the Teen Mom dads: Who's the worst?

It seems like just yesterday the Teen Mom tots were in diapers, crying and unable to hold their own heads up. Now? They're talking, walking and well, they still cry, but they remain pretty darn adorable.

Before Teen Mom OG premieres (Monday, March 23, 10/9c, MTV), look back at the way Leah, Carly, Sophia and Bentley — and (bonus!) the Teen Mom 2 kids — were and what they look like now below.