Bruce: Kourtney Is “Growing Up” After Having Baby

 Albert Michael/

When it comes to being a good mom to baby Mason, Kourtney Kardashian has surprised even her own family!

"She's taking motherhood so seriously — to be honest, even I'm a little amazed," stepdad Bruce Jenner tells "She's breastfeeding so she has to be pretty much with Mason all the time anyway, but she really is taking it seriously and she’s doing an amazing job."

He is most impressed with how Kourtney, 30, has matured since giving birth to her son in December.

"You know, Kourtney has always been kind of a free agent — she does what she wants to do," Jenner told Us at a COPD charity event in NYC Wednesday. "She’s gone from being a young person with very few responsibilities to an adult, with some major responsibilities, and she’s really growing up."

He says "it's been fun" to see her do "a wonderful job" raising her son.

Kourtney isn't the only one that has impressed him. In addition to "built-in babysitters" with Kim, Kylie and Kendall, he says Scott Disick is "really coming through" as a new dad.

"He’s still a work in progress, don’t get me wrong, but he’s coming along," he admits. "You never know how someone is going to handle such big responsibility, but they are doing a great job, both of them are."

As for the littlest Kardashian?

"Mason’s just getting more and more aware and growing just beautifully," Jenner tells Us.

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