Roald Dahl's daughter on when "The BFG" was a bedtime story

Roald Dahl's fantastical stories have captivated the imaginations of children across the globe for decades. The latest Steven Spielberg big-screen reimagining brings to life one of Dahl's most cherished tales, "The BFG."

But imagine what it must have been like growing up in that world, a world of make-believe.

Lucy Dahl doesn't have to. As daughter to the famous author, she had a front row seat.

CBS News correspondent Charlie D'Agata spoke to Lucy at a Roald Dahl tour for children in London celebrating 100 years since the author's birth.

"So you were the original audience for the BFG?" D'Agata asked her.

"The BFG was one of us. The BFG lived under the orchard that was beyond our garden. ... He lived there, he slept there, he concocted his dreams," Lucy said.

She grew up in an idyllic cottage in a little village outside the capital, where nearby woodland was home to the "Fantastic Mr. Fox," "James and the Giant Peach" and other friends.

Every night, Lucy said, her father would tell her and her sister, Ophelia, bedtime stories -- rough drafts of the tales that would one day make it into print.

"He told us later on that if we would say at the end of a 20 minute story, 'All right, thanks, 'night,' it wasn't a very good idea. If we said, 'No, no, no, no, please, please! Go on, go on, go on! Tell us some more tomorrow!' then he would think, 'Hmm, I'm on to something!' That was what happened with the 'BFG,'" Lucy said.

Like everything else in little Lucy's world, the Big Friendly Giant was not wholly fictional.

"This is Wally Saunders," Lucy described, holding a photo of a man. "And he was our great family friend. When Quentin Blake was drawing the BFG, my dad said, 'Quentin, it's not quite right, hold on one second,' and he went outside and he called to Wally. Wally came in and dad said, 'Quentin, look at this man, look at his fantastic features. Look at this ears, look at his nose."

But Dahl's subject matter was definitely not all sweetness and light.

"There is a hint of darkness in your father's stories," D'Agata pointed out.

"Without question, yes," Lucy said.

"Because there has to be?" D'Agata asked.

"Children like to be scared a little bit. Not much. Not enough for nightmares. They don't like everything to be lovely all of the time. So there's a very fine imaginary line to the dark side and not the dark side. You go as dark gray as you possible can and then you stop," Lucy said.

Which is why, in Roald Dahl's world, even giants lurking in the shadows can be friendly.