AceShowbiz - Madonna has proudly called her twin daughters "Kweens" at their elementary school graduation. The Queen of Pop, 64, celebrated 10-year-old Stella's and Estere's big day by sharing a photo of the pair on her Instagram stories showing them grinning and holding two bouquets of flowers.

"2 Kweens!!!! Happy Graduation!" Madonna captioned the image of her girls wearing blue caps and gowns.

Stella and Estere are the "Material Girl" singer's youngest children, whom she adopted from Malawi six years ago. She also has daughters Lourdes, 26, and Chifundo, 17, and sons Rocco, 22, and 17-year-old David.

Additionally, Madonna adopted David and Mercy from Malawi in 2008 and 2009, and she had Lourdes with her ex-partner Carlos Leon, 56, and Rocco with her 54-year-old film director ex-husband Guy Ritchie.

Madonna recently told Variety growing up with her as a mum is "difficult." She added, "Growing up with a mother like me is a challenge. It has been the most difficult, the hardest battle. Because, whoever you are, having children and raising them is a work of art. And no one gives you a manual. You have to learn from mistakes. It is a profession that requires a lot of time. And it is exhausting because there is never rest."

Madonna has also shared updates with her fans about rehearsals for her upcoming greatest hits tour and captioned her most recent set of snaps on Instagram showing her preparing for the gigs, "Calm before the storm… ."

Madonna - who first entered the US Billboard Hot 100 with 1983's "Holiday" - last July said about how she was keen to get back on stage, "I want to go on tour again. I'm a creature of the stage. That's my happy place."