Michelle Obama's daughters are growing up fast - and on Monday Malia Obama marked her 24th birthday.MORE: What Malia Obama is really like to work with as she moves to LAProud mom Michelle marked her firstborn's special day with a heartfelt tribute posted on Instagram.The former FLOTUS shared a sweet throwback of herself with Malia as a baby, alongside the message: "Happy birthday, Malia – and Happy Fourth of July, everybody!VIDEO: Michelle Obama opens up about her daughters Malia and Sasha"24 years ago, this day became extra special when your wonderful spirit arrived in this world. I’m so proud of the beautiful, caring, and driven young woman you’ve become.