Katherine Schwarzenegger Reveals Biggest Change When It Comes to Having 2 Kids With Chris Pratt (Exclusive)

The author and adoring mom spoke with ET about her life, her family and her new children's book, 'Good Night, Sister.'

Katherine Schwarzenegger and Chris Pratt are still settling in to life with two tiny daughters, but they are making it work -- and using the experience for inspiration!

Katherine sat down with ET's Rachel Smith in New York recently, while promoting her new children's book, Good Night, Sister, and she opened up about having recently welcomed a new baby girl last May.

"We are hardcore adulting here!" she said with a laugh. "It's been a very blessed time. I feel very lucky."

Katherine shares two daughters with Chris -- Lyla, 2, and Eloise, 8 months, as well as Chris' 10-year-old son, Jack, from his previous marriage. However, having an infant and a toddler has come with its challenges.

"It's wild! I mean, I think that to me the biggest adjustment has been just the sleep factor. I feel like everybody always tells me that the jump from one to two children is the biggest," she shared. "I don’t know if it's because I’m the oldest in my family that I didn’t really feel like there was more commotion going on or more activity, 'cause I’m used to that, but definitely in the middle of the night, when they both wake up, is when I’m just kind of like, 'OK, this can be a lot.'"

Although, she's getting all the love and support from her husband, who has really enjoyed being a father to two adorable little girls. Katherine gushed, "It's so sweet to watch! He's an incredible dad... it's very special."

The adoring mom said Lyla is also a very loving and caring older sister, even at 2.

"She is just so excited about her all the time, wants to be with her, wants to squeeze her, wants to hug her, help her," she explained. "Just the two of them are just so sweet together."

The relationship she's seeing develop between her daughters has made her feel even closer to the subject matter of her new book, Good Night, Sister, which details the importance of a sisterly bond.

"It's really special to be coming out with something that talks about the importance of sisterhood and just the importance of that relationship, because it was such an amazing one growing up, and to be able to read so many of the same books and do so many of the same things that I did with my sister," she explained. "To watch my girls do the same is so special."

Katherine has had a similar relationship with her younger sister, Christina Schwarzenegger, and is looking forward to sharing stories about that closeness -- something she's relied on with the newest addition to her own family.

"I'm so lucky with my whole family and how they've all stepped into these roles as aunts and uncles and, you know, my parents are grandparents," she explained. "My mom and my dad are both amazing grandparents to my girls and to see them all here now is so special."

"They just really love the grandparent role," she added. "Especially [how] you can hype them up on sugar and send them home."

For Katherine, her mom, Maria Shriver, has been a particular source of strength and inspiration during her own parenting journey.

"I always watched my mom, growing up, just being the epitome of strength, class, beauty, resilience, and you know she always had fun as a mom," Katherine reflected. "She’s an incredible mom, incredible wife, daughter, friend, everything."

"To this day I just am in awe of my mom constantly," she added. "I think she is just incredible and I strive to be a little bit like her all the time. I ask her for advice on parenting 100 times a day."

Katherine's new illustrated children's book, Good Night, Sister, comes out Feb. 7.