Irwin, who welcomed her baby girl Grace on March 25, shared a touching note on Instagram.
"Celebrating my first Mother’s Day," Irwin wrote alongside images that brought her and husband Chandler Powell's families together -- including her late father, Steve Irwin.
"This day embodies the extraordinary gift of family. Thank you to ‘The Monkey Brush’ for bringing my family and Chandler’s together in these stunning works of art. I wish we could all be together but sometimes life has other plans. ❤️To my beautiful daughter, always know that you are loved beyond description."
Hadid, who announced in September that she had given birth to her first child, also celebrated her first Mother's Day.
"The rumors are true: my best friend, purpose, muse, greatest pride & joy! I" she wrote alongside photos showing her with Khai, who she shares with Zayn Malik. "I feel so lucky and inspired bein your mama, my Khai !! An old soul full of sunshine, you light up everyone’s days! Thank you 🧡 thank you 💛 thank you 💕."
Gabrielle Union reflected on her difficult journey to motherhood in her post, sending her thoughts to those who may be struggling on the holiday.
"My journey to motherhood was long, arduous and at many times extremely painful. Mother's Day will always be a challenging day to celebrate for me. I know I'm not alone in this feeling. For many reasons, so many of us have a rough time today and to these good people, I send all my love, light and compassion," she shared. "To all the Moms, Stepmoms, Bonus Mom's, Folks who Mother those that need it, Grandma's, House Mothers, I celebrate you today and everyday. Be good to yourselves. 🖤🖤🖤 ."
Jennifer Lopez called being a mom her "greatest joy."
"It was my mom who instilled in us at a very young age that we could do anything. This was something that has really stayed with me. Being a mom is my greatest joy, and today I think about my mommy and all the moms out there. This is your day, and I hope you are surrounded by love, gratitude and appreciation…enjoy it! #HappyMothersDay #IGotItFromMyMama #MamaGlowsBest," she wrote on Instagram.
"It can’t be said enough… you’re the heart and soul of every moment this family shares," Ryan Reynolds wrote in a tribute to his wife, Blake Lively. "I’m grateful for the light and for the kindness you smuggle into each and every second of our lives. I see you in the eyes of our children… Every laugh. Every blink and every thoughtful moment of vulnerability. The tender grit it takes to be a mother in 2021 is an act of pure strength and heroism. Never could I have predicted anonymous airport bathroom sex would lead to this. Or how you’d hire Dog The Bounty Hunter to find me. Either way, I’m lucky to reflect a little of the sunlight you shine on all of us. Happy Mother’s Day, my love."
Joe Jonas also took to Instagram to share a special tribute to his wife Sophie Turner and mom, Denise. "Happy Mother’s Day to all the amazing mother’s out there and to these two Mums," he wrote.
See more celeb posts below.