In 2006, when Pixar and Disney merged, the first thing “Toy Story 3” helmer Lee Unkrich did was scrap Disney’s in-the-works version of “TS3.”

“We kind of felt like our children had been taken away from us and were being raised by strangers,” said Unkrich, who also co-directed “TS2.”

Unkrich tapped Michael Arndt, who had just wowed Sundance with “Little Miss Sunshine,” as scribe. Then he organized an off-site, brainstorming session with several members of the original “Toy Story” team, including Andrew Stanton and John Lasseter, in which a story skeleton was drafted.

They returned to Pixar with a 20-page treatment, which Stanton handed off to Arndt. Arndt then took three years, and several dozen drafts, to craft the final script.

Unkrich was wracked by doubts that he’d live up to the first two “TS” pics. With the exception of “Godfather III” and “Lord of the Rings: Return of the King,” the third movie in a series rarely sees the critical acclaim awarded its prequels.

“We felt (a) crushing responsibility,” he said. “We didn’t want to be known as the guys who screwed it up.”

As for his frosh scribe, however, he was confident. “Everyone was on board with having Michael write this movie even though it was this treasured property,” he said. “We trusted him.”

Arndt was a quick study. “The ‘Little Miss Sunshine,’ process was me sitting in my backyard building a little homemade rocket. And going to Pixar and writing ‘Toy Story 3’ was like going to work at NASA,” he said. “It’s sort of the same thing but not really.”

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