Bell is the widow of the actor John Mills and the mother of actresses Juliet and Haley Mills.
Her grandson, Crispian Mills, is co-writing the script for "The Winged Boy," which is being directed by Luis Mandocki, the Hollywood Reporter said Monday.
"The Winged Boy" will be a family film about an Irish boy who grows wings and learns to fly, the Reporter said.
The film is scheduled to start shooting in Ireland in the spring.
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