According to The Twilight Saga: Breaking Dawn Part 1 IMDb.com, 5-year-old Eliza Faria has been cast as Little Renesmee -
All these are from Breaking DawnMovie Here are more information on Eliza -
Five year old, Eliza Faria, began her acting career when she landed her first role in a Lysol Disinfectant commercial at the age of two. Her subsequent TV commercial work includes Cisco The Human Network and Hasbro Scatterpillar. Read more about little Eliza here
Interesting! We are not exactly sure what they’ll be using her for as Mackenzie Foy is officially cast as Renesmee. We are thinking she must be the “body” they are using, and then Mackenzie’s head as CGI?
UPDATE: Rumor has it that there will be several Little Renesmee’s, however Eliza is the only one listed thus far.
More on the CGI technique that will be used for Renesmee.
MackenzieFoy.com "We have more information about the techniques of CGI, which should be used in Breaking Dawn to the rapid growth of Renesmee (the character played by Mackenzie). CGI's team used a combination of "Motion Capture" photography and live action. " They put a cap on the Mackenzie equipped with a small camera that was placed in front of your face. As in "Avatar," the information gathered from their facial expressions and your eyes will be transmitted to computers.
As stated earlier, the face of Mackenzie will be transferred digitally to a body of a girl to create the illusion of rapid aging of her character. Besides the data collected directly to the computers, cameras give numerous reports from various angles digital. All the live action and every movement will be captured for the screen."