Jessica Simpson Raves About Daughter Maxwell on Her 9th Birthday: 'Her Inquisitive Mind Strengthens Mine'

Jessica Simpson's eldest child, daughter Maxwell Drew, turned 9 on Saturday

Photo: Jessica Simpson / Instagram

They grow up so fast.

Jessica Simpson celebrated her daughter Maxwell Drew, who turned 9 on Saturday. "Maxwell, my best friend and first born, turned 9 yesterday, May 1. If any of you have read my memoir, OPEN BOOK, or my Amazon essay, TAKE THE LEAD, then you have a sense of my forever baby girl (even though she will be taller than me in about 6 months and shares my shoe size)," the fashion designer, 40, shared on Instagram Sunday, along with a photo of her family.

Raving about her oldest child, Simpson continued, "She is prayerful, nurturing, intuitive beyond belief, hilarious, honest, a lover of horses and every animal on the planet, empathetic, wise beyond her years, thoughtful, strong, beautiful, hardworking, creative and observant (which makes her one of the most epic impersonators to make anyone laugh), she is a prolific writer of poem and songs, and she listens and trusts herself with confidence I admire."

Simpson and husband Eric Johnson are also parents to son Ace Knute, 7, and daughter Birdie Mae, 2.

Concluding her tribute post, the mom of three praised her daughter Maxwell, writing, "The energy in a room shifts when she enters. Yes, she is the most beautiful I ever did see, but it is the effortless way she holds her power that is unlike anything I've ever seen. Her inquisitive mind strengthens mine. Her heart holds space everyone and everything. When I think about her I can't help but smile with all that I have, a happy smile is always inspired by her, the possessor of the most genuine, pretty, sometimes cheeky but always the purest of smiles ever to grin. My favorite hands to have and hold in prayer or just in life are hers, always my daughter. She loves you enough to be the person you have always wanted to be. I am constantly in awe of her resilience and grace, it is amazing indeed. I love her beyond measure. Happy belated (to Instagram) birthday Maxi!"

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Simpson recently reflected on how her daughter helped her conquer her fear of horses during a photoshoot they once did together.

"She wanted one of the horses that she rides to be in a shoot. This was her way of [being] like, 'I'm gonna make Mom ride this horse,' " the Open Book author recalled during an interview with Today's Hoda Kotb last Thursday.

"She was like, 'Horses know that you're afraid, Mom. And it's not gonna relax until you put your shoulders down and breathe. And Mom, let's just stand at the mountain and scream over the mountain,' " she added.

Afterwards, Simpson said that her daughter "handed me the reins and gave me the lead," which she described as a "beautiful moment" — at least, until "the horse emptied out like four days worth of pee."

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Simpson recently told PEOPLE that during the COVID-19 pandemic she learned a lot about herself — and how resilient her children are.

"In many ways, they were the peaceful force that made life precious in this trying time," said Simpson, who revealed in March that she previously tested positive for the virus. "I absolutely had moments where I was just in tears and so overwhelmed, but I got through them."

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"I think the takeaway is that it's not easy and every day presents challenges and blessings," she added. "Life is a blessing to be lived, and the more we overthink things, the more we fall behind on our personal journey."