The daughter of the tennis player and Home and Away actress turned thirteen last November.
Bec shared a post on Instagram of her lookalike daughter for her birthday.
"This beautiful soul has spent 13 years on this Earth! I’m so grateful to have her in my life everyday! I’m a real believer that our kids are here to teach us as much as we teach them! I am always learning from Mia! How to be patient, how to be positive and how to be a better person. She is beyond her years! Such a kind, gentle, intelligent, calm yet bubbly person to be around! Happy birthday to my beautiful daughter and friend! Enjoy your teenage years!" The Dancing with the Stars contestant wrote in the caption.
Mia also joined mum Bec in a campaign for Palmolive Naturals Haircare last year.
The Hewitt girls posed together in a series of photos for the brand, which Bec shared with her Instagram followers.
"We’re so excited to finally be able to announce that Mia and I are the new Ambassadors for Palmolive Naturals Haircare! We had so much fun working together on this campaign. So proud of my girl!" The Hello World ambassador wrote.