Reese Witherspoon attends the 'Sing' Red Carpet Premiere for the 2016 Toronto International Film Festival Premiere at the Princess of Wales Theatre on September 10, 2016 in Toronto, Canada.
Credit: Walter McBride/Getty

Reese Witherspoon's son Tennessee celebrated in his fourth birthday on Sunday, and the proud mom took to social media to document her youngest's seriously epic Teenage Mutant Ninja Turtles party.

"Celebrating someone VERY special's birthday today!!! (Two hints: he is a #NinjaTurtles fan and this is his cake ... )," the Wild star wrote alongside a close-up shot of a themed lilac birthday cake which has the tot's name "Tennessee" on it, as well as a bunch of Skittles, stars, and little Teenage Mutant Ninja Turtles toys that appear to be coming out of the cake.

She then took to her Instagram and Twitter accounts to share a photo of the little tot, who is dressed in yellow drawstring pants and a gray T-shirt, holding a red balloon in front of a door while text saying "Tennessee turns 4!" is splashed across the picture in yellow lettering.

"This smile says it all! Had such a special day- celebrating this sweet little one's (soon-to-be) birthday!!! We love you so much Tennessee!!!" the mom-of-three wrote, adding the hashtags #TimeFlies and "SundayFunday.

Mom Reese wasn't the only one to wish the little toddler a happy birthday on social media. Big stepsister Ava Phillippe, 17, who Witherspoon shares with ex-husband Ryan Phillippe, took to her Instagram account to share a close-up shot of her little brother sipping from a juice box.

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"[H]appy early birthday to this super preschooler going on teenager. I love you, dude," the teen captioned the sweet photo.

Time sure does fly!