The Ek Tha Tiger star will play a character with special powers, sporting shoulder-length hair, in the film directed by his brother Sohail Khan.
A source told the Mumbai Mirror: "Kona Venkatesh who wrote Salman's Ready was originally enlisted to write the screenplay for the film.
"Now, Sohail and Salman have changed their mind. They roped in Rumi Jaffery to write an action film for the kids instead."
Speaking about the decision to make a film for children, Jaffery said: "Though he has had a massive fan following among kids, none of Salman bhai's films have been specially targeted at children.
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"Dilip Shukla and I are designing bhai's first film aimed at the young viewers. He will be a hero that kids can identify with.
"The action scenes won't have him beating up a dozen goons single-handedly. He has done these things many times before."
Khan's action scenes will be inspired by the ancient forms of martial arts from Kerala. The leading lady opposite the superhero is yet to be finalised.
"It has to be someone who can perform well, " explained Jaffery. "Since Salman bhai is changing in Sher Khan, the leading lady can't be familiar either. We're looking. We have time. We start in October."
Sohail Khan has said he plans to make the film in 3D.