Mandy Moore Honors the 'Greatest Gift' of Being a Mom as She Celebrates Son Gus' Third Birthday: 'So Lucky'

The actress shares her two sons, Gus and Oscar, with husband Taylor Goldsmith

Mandy Moore is celebrating her little guy's big day!

On Tuesday, the This Is Us actress, 39, shared a Reel on Instagram in honor of her son Gus' third birthday. Sharing photos of her son from throughout the past year, the toddler smiles, laughs and poses with his little brother Oscar "Ozzie," 16 months.

"3! How in the world has time flown so fast? You amaze us in every way, Goosey," the proud mom wrote in her caption.

"Your smile lights up every room, your curiosity about the world around you evolves daily, your obsession with construction vehicles continues to grow with a fervor, your tender heart and love for your family, including your brother (in between clocking him with a random toy of course) melts us…. We are so lucky."

"Thank you for the greatest gift of being your mom. Cheers to more laughs, trucks and gummies, my sweet boy. We 💓 you!!! Happy Birthday!!" Moore concluded her post.

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Related: Mandy Moore's Holiday Plans with Her Family Include Being 'Home and Cozy' (Exclusive)

In December, the mom of two shared with PEOPLE what she was most looking forward to during the holiday season.

"I'm excited for these next couple of weeks just to be home and cozy and enjoy this time of year," Moore said at the Dr. Death season 2 premiere in West Hollywood.

This season marked the first year that Moore and Goldsmith's oldest son, Gus, really began to understand the festive season. As a result, the mom of two was seeing Christmas through her little one's eyes.

"He's loving being a big brother and he is loving the holidays," Moore said. "Now, he's aware of it in a way that he wasn't until this year, like last year, he was just sort of starting to grasp Christmas trees, but now he understands the concept of Santa and all of that is it's so much more exciting."

Earlier that same month, Moore appeared on The Tonight Show with Jimmy Fallon and revealed that although she's well known for playing Rapunzel in Disney's Tangled, her older son doesn't seem to care.

"He couldn't have cared less," she told host Jimmy Fallon of her son's disinterest in the 2010 animated musical film.

"He's like, 'You're not Lightning McQueen.' There's no Cars situation," she went on, noting Gus' preference for the Pixar film series and protagonist voiced by Owen Wilson.

"I have asked him several times. I'm like, 'You've seen Frozen now — do you want to watch Tangled?' He's like, 'No,' " Moore said, laughing. "It means nothing to him!"

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