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Kourtney Kardashian's son Mason Dash Disick isn't so little anymore -- he's growing up so fast!

Today Kim Kardashian tweeted some adorable pics of herself with the birthday boy and wrote on her blog, "I can’t believe Mason is turning three today! He has changed my world in so many ways and I am amazed every day by him. He is the world’s greatest big brother to Penelope and the most loving nephew any aunt could ask for."

Wonder what she got him? And when is she going to start her own family with beau Kanye West? Apparently she's already thinking about it...

Click thru for another shot of Mason and his auntie!