It turns out that 17-year-old Ava has already been mistaken for her Oscar-winning mother.
"I had a premiere for that movie Sing! over Christmas, and the head of the studio went up to Ava and congratulated her on the movie," Witherspoon revealed to ET’s Nischelle Turner. "But I just love her. I'm so lucky to be her mom, and I just love having her in my life and getting to go everywhere with her. It's a great honor."
Mother and daughter look so much alike that it's even hard to tell them apart in a snap shared by the 40-year-old actress on Instagram last week.
"Me and my girl," Witherspoon captioned the sweet pic.
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"I'm like, what is this thing on Instagram, and what does it mean with this hashtag?' And she's like, ‘Oh that's this,'" Witherspoon shared before calling Newton "awesome."
Parenting wasn't the only topic on Witherspoon's mind. The mother of three also discussed reteaming with her Wild co-star, Laura Dern, and their quest to get a laugh out of another of their Big Little Lies co-stars, Nicole Kidman.
"We hate each other," Witherspoon said of her and Dern's characters in the limited series, which premieres on HBO on Feb. 19. "It was so fun because she and I love to do comedy, and play, and riff off each other, so I was trying to think of the nastiest things we could say to each other just to make Nicole Kidman laugh."
She may appear buttoned-up, but Witherspoon revealed that she's an apparent pro at getting dirty for the sake of comedy.
"I pretty much topped her by episode two," Witherspoon said of Dern, adding that she got a laugh out of Kidman by being the "dirtiest" that she's ever been.