James Cameron and 20th Century Fox announced a total of three sequels to the 2009 film last summer.
They'll rejoin Stephen Lang who has signed on for the sequels as well. Lang played main antagonist Marine Colonel Miles Quaritch who was killed off in the 2009 film.
"Avatar" demolished box-office records in 2009 when it became the highest-grossing movie of all time making $2.8 billion worldwide.
There's not much news on the plot of the film, but THR reports Saldana and Worthington's characters, Sully and Neytiri, will have kids.
The films are expected to come out back to back in December 2016, 2017, and 2018.