Due to Roald Dahl's distaste for Willy Wonka & the Chocolate Factory (1971) and The Witches (1990), the Dahl estate initially barred a Matilda movie
Robin Swicord (screenwriter): [My husband and writing partner Nicholas Kazan and I] said, "How about we write this for free? If you do like it, we'll go out together as partners." Liccy Dahl, his widow, was open to working that way. She couldn't sell it to anyone else until she'd seen our screenplay. [...] Nick and I wrote it together, over a summer. Our children and friends who were there read it aloud to us and we could hear it. It was a wonderful family thing. We had to give it to her by September and we did, and she said, “This is fine, let's go.”
DeVito directed the film for his kids
Swicord: He cared enormously. His kids loved the book. That whole thing that had happened in our family was also happening in his [...] He wanted his wife [Rhea Perlman] in the film. He wanted to narrate it, which I felt was kind of confusing at the creative level in terms of, "Why is it the father's voice? Why is Matilda's father telling her story?" It felt like it should be more like the voice of God. It should be Roald Dahl's voice? But, you know, it was personal for him. I really appreciated that.
The famous "you're not alone" line wasn't written by Roald Dahl -- though it's credited to him
Swicord: That's a line that I wrote. That's not a Dahl line…The library was my solace. It was the thing that connected me to the larger world. I knew that I was a writer very young, as soon as I learned to read I knew that I was a writer. I felt that the books that I was reading were literally the voices of authors who were calling me forward out of the world that I was in.