See Reese Witherspoon's sweet birthday tribute to 'littlest guy' Tennessee, 5

Reese Witherspoon's youngest child is growing up.

On Tuesday, the "Big Little Lies" Emmy winner shared a heartfelt message to her adorable son Tennessee on his 5th birthday.

The 41-year-old actress took to Instagram to share a pic of her little boy — whose dad is Witherspoon's hubby, talent agent Jim Toth — gleefully grasping a colorful balloon in the shape of the number five.

"Happy Birthday to my littlest guy , Tennessee! Every day you bring us so much joy with your sweet smile and beautiful laugh. I love you so much!" Witherspoon wrote in the caption.

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Jennifer Aniston and Reese Witherspoon team up for new TV series

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Jennifer Aniston and Reese Witherspoon team up for new TV series

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It's been a month full of happy celebrations for the Oscar winner, who has two older children, look-alike daughter Ava, 18, and son Deacon, 13, with ex-husband Ryan Phillippe, 43.

18 letters that made me cry (hard) today, courtesy of my lovely mother.

A post shared by Ava Phillippe (@avaphillippe) on

On Sept. 9, Witherspoon helped Ava ring in her 18th birthday by giving her the most thoughtful gift ever — a collection of 18 handwritten letters from mom, one penned each year on the teen's special day.

Witherspoon also posted the sweetest throwback photo with her mini-me, gushing, "Your kindness, grace, intelligence and humor never cease to amaze me....I feel so lucky that I get to be your mom."

Chris Pizzello / AP
"Big Little Lies" stars at the 2017 Emmys: (L-R) Shailene Woodley, Nicole Kidman, Reese Witherspoon, Laura Dern and Zoe Kravitz.

Just days later, Witherspoon got to celebrate all over again when she and co-stars Nicole Kidman, Zoe Kravitz, Laura Dern, Alexander Skarsgard and Shailene Woodley nabbed the Emmy for Best Limited Series for HBO's smash hit "Big Little Lies."

Kidman, Skarsgard and Dern also won individual acting awards for the series, which talented Witherspoon produced.

What a happy month for Reese and her family!