On Tuesday, the 42-year-old "Predator" actress took to Instagram to share a candid video of her almost-one-year-old son, Malcolm, whom she shares with comedian John Mulaney, dressed up as her mother, Kim Munn.
In the "hilarious" clip, Malcolm is sitting on a sofa next to a box of Wheat Thins crackers and a container of sunflower seeds while holding a long pepperoni stick. He also wore blue flip-flops, red floral pants, a grey T-shirt and a black bob-cut wig.
"Happy Halloween," the on-screen text reads. "He hated this wig."
In the caption for the post, Olivia added a quippy note for her more than 2.7 million followers.
"Malcolm dressed up as the most iconic figure in his life... my mom," she wrote.
The "X-Men: Apocalypse" star also shared a photo of her mother in an Instagram Story for reference, where Kim wore a similar hairstyle and outfit, while sitting on a chair with a box of crackers, a bag of sunflower seeds and a long pepperoni stick.
"Identical," Olivia wrote as on-screen text to the photo.
In the comments section of the video, fans and loved ones of Olivia shared their appreciation for the sweet post.
"Again, I think we should keep him in this costume for a few weeks," Mulaney shared.
"Lol! This is hilarious and adorable. Shout out to grandma! He actually looks just like her, it's uncanny haha. So cute," one person wrote.
"So good!" another added.
"I about died when his costume reveal came up. Can we talk about the resemblance to your mom with the wig?" someone commented.
One Instagram user shared, "This absolutely 100 per cent made my day! What a memory."
"Malcolm won Halloween! The entire thing is amazing," a fan chimed in.
In August, Olivia playfully addressed all of her missed text messages, while addressing one of the stresses that comes with being a new mom — breastfeeding.
"I'm in a teething tunnel nightmare," she wrote as on-screen text on the Instagram Reel.
"This will also serve as a group text to anyone I haven't texted back. I will get back to you in however long it takes for this tooth to come out," she captioned the clip, where she zooms in on her face as "Help!" by The Beatles played.
The actresses message was met with praise from fans who opened up about their own struggles with similar issues.
"Teething was brutal. You'll be OK. Just drink a lot of coffee. That worked for me," one Instagram user penned.
"I remember those days with mine! It's tough. You will get through it!" another echoed.
One fan shared, "I've been waiting for my eight-month-old baby's teeth to come out! Teething is the worst!"
"We are right in the middle of this battle as well! Hang in there," commented another.