Britney Spears' two adorable sons -- Sean Preston and Jayden James Federline -- both celebrate birthdays this week.

Sean Preston turns six today, while Jayden James celebrated his fifth birthday on Monday. Time sure flies fast -- it seemed like just yesterday that Brit was driving down the freeway with baby Sean Preston on her lap. Click on the "Launch Gallery" button to see photos of the boys through the years:

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The boys' father is Britney's ex-husband Kevin Federline. Kevin recently welcomed his fifth child, a girl, in August. Sean Preston and Jayden James have warmed to Jason Trawick, Britney's current beau. In April, the family took a vacation to Las Vegas, where they saw "The Lion King."

Britney posted a message to her firstborn on Facebook today that read: "Preston Happy Birthday! My little baby is growing up so fast. I love you. Mommy." She posted a similar message to her youngest on Monday: "Happy Birthday Jayden! Mommy loves you so much."

Happy birthday to both boys!