Thomas Rhett and Lauren Akins Celebrate 'Angel' Daughter Willa's 6th Birthday: 'You Are a Joy'

Thomas Rhett and Lauren Akins' daughter Willa is celebrating another trip around the sun.

On Tuesday, the country singer and his wife, both 31, honored their oldest daughter Willa for her 6th birthday. Akins shared a series of photos on Instagram, including a snap of Willa catching snowflakes with her parents and a sweet shot of the family of five posing on the beach together in matching outfits.

"Without a shadow of a doubt you bring our family average UP Willa Gray just by shining your bright light ✨💕," she wrote. "You are a JOY to parent and you love people so well-especially your little sisters 🥰

Akins continued, "Your kindness is one of the sweetest gifts to this world and the last 6 years the world has been a better place by having YOU in it! Happy 6th birthday sweet angel baby! I am so proud of who you are and you are SO loved 💗🎈💗🎈💗."

Thomas Rhett also penned a sweet message, sharing a photo of Willa wearing a white dress and gold crown for her birthday party.

"Willa Gray.. how in the world are you already 6????? I love you more than life," the singer captioned the post. "You are the best big sister any sister could ask for. You make me a better person just by smiling. Your smile could light up any room. I love getting to be your daddy. Happy birthday sweet baby🙌."

Akins and Thomas Rhett, who are also parents to daughters Lennon Love, 20 months, and Ada James, 4 — and are expecting their fourth child together this month — welcomed Willa home from Uganda in 2017.

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In April 2016, Willa — known then by her nickname "Blessing" — was just one of many orphans in a children's home Akins visited while working in Uganda with the Christian charity 147 Million Orphans. At the time, the couple had been trying to get pregnant with no luck, and had just begun to consider adoption.

"She really does live up to her nickname in Uganda: She is just the biggest little Blessing that ever has walked the earth," Akins previously told PEOPLE of the toddler, who'd been brought to the children's home soon after her birth in November 2015.

In the years since they adopted Willa, the couple has strived to teach their eldest daughter to embrace herself for who she is.

"[It's] something that we talk about really openly," the country singer told Entertainment Tonight last September about the conversations they've shared surrounding the fact that Willa has noticed that her family "looks a lot different" than others.

"I think me and Lauren's main thing we want to get across is how proud we are and that we want her to grow up proud of herself and of her family," he said. "[We tell Willa] to embrace who you are and to embrace your uniqueness and embrace your culture as well."

Thomas Rhett added, "That's something we want to educate her on as long as she's still in our household and even beyond that."