On Saturday, the actress took to Instagram to honor her eldest child, posting several throwback images.
"My sweet first born came on your due date ready for action and have been in the drivers seat ready for this journey from the day you were born!" Demi captioned a photo of Rumer as a baby pretending to drive a car. "Happy Birthday Baby Ru! Before you I didn't really know what love was! You continue to light the pathway of loving and I am honored to be on this ride with you my angel!"
She added, "Thank you for being a beautiful teacher and a magnificent being. I love you beyond measure!"
Demi later shared another image of herself sleeping with baby Rumer.
Rumer's sisters, Tallulah Willis and Scout Willis, also got in on the act.
"My strength, my valor, my tenderest hearted mama Rue, you walk into today a year older, with every single one of us in your corner. I am honored to have been chosen to walk this earth beside you, to learn from and with you, to share near-pants-peeing laughter, and bottomless movie marathon sprints," Tallulah captioned a throwback snap.
"You always win, but I can try to keep up," she continued. "You are radiating from a place of unbelievable emotional intelligence and with your actions show the rest of us a way to be that comes from solely a loving place. You are you and that is exactly perfect. You are the sexiest 31 year old this world has ever seen. Clear eyes, full hearts, cannot ever lose."
Scout posted a series of throwbacks to honor her sister, as well.
"You are a queen, you are flourishing, you are growing into your final Pokémon form, and damn it's sexy, it's intelligent, it's caring, it's mature, it lets me briefly yell at it to express my anger all the while knowing it has nothing to do with her," she wrote. "You are the most generous human being I know, you give all of yourself to those you love and all you ask in return is for me to sleep over at your house bi-weekly and sog our with you."