It has become vogue for film-makers to look back, not forward. Directors of big movie franchises such as Star Trek, Star Wars, Batman, Superman, Lord of the Rings ask the question: "How did these characters become what they've become?"
Which is precisely the question being asked by the animators at Disney/Pixar about Mike and Sully, the monster pals in the monster hit, Monsters Inc.
How did Mike, the one-eyed beachball with legs, become friends with Sully, the blue-furred, dragon-tailed ape-y thingy? And how did they end up working as Scarers at Monsters Inc., the company that scares the wits out of slumbering children? They went to Monsters University, of course. Good, eh? Wish I'd thought of that.
It might be a predictable premise, but my sons, aged eight and five, didn't care: they loved Monsters University, from the moment a schoolboy Mike visits Monsters Inc. on a school trip, right through to the end when he and Sully land their dream jobs.
Yes, that's giving the end away – but you already knew that, didn't you? Because it's a prequel.
It's what happens in between that so enjoyable. At its heart, Monsters University is a morality tale with the simple message: if you work hard, you will succeed, whatever your background.
As the conduits for that message, Mike, voiced by Billy Crystal, longs to be the scariest monster of them all but is burdened by the physical fact of him being rather affable and very geeky, whereas Sully (John Goodman) is from a 'privileged' background because his dad was a Super Scarer and thus Sully is expected to follow in the family tradition.
And further thus the rivalry is set: the ordinary kid with ability and desire vs the silver spoon jock with no ambition.
They both end up at Monsters University and, unsurprisingly, can't stand each other. But after months of undermining each other, they end up upsetting the genuinely terrifying Dean Hardscrabble (Helen Mirren) – a cross between a winged dragon and a centipede - and are thrown off the scarer programme.
The only way back is if they can win the annual team-scaring competition – and the only way to do that is to work together.
You can imagine – or see – the rest for yourselves – but as much as I found the movie an easy way to spend a couple of hours with my eight-and-five-year-old son, I found it rather forgettable compared to other Pixar classics (the 'Toy Story' trilogy, 'Up', 'The Incredibles' and my all-time favourite animated film, 'Wall-E', spring to mind).
It lacks the charm of its predecessor (or successor, depending on how you look at it), Monsters Inc. because there are no relationships between the monsters and the human children they're supposed to terrify. There's no-one to root for because it's hard to relate to animated composites of different animals and insects.
But what do I know? My two sons declared it 'Awesome' and there were at least half a dozen kids in the cinema where we saw it who were bawling their eyes out and begging to be taken home because they were scared (as they should be!).
But for me, it was a bit too 'knowing' of the adult student world (frat parties and campus in-jokes) and not connectable enough with the little 'uns who will be pestering their parents to see it.
Monsters University is released on July 12.
A new range of Monster toys has been released to celebrate Monsters University - including a Sulley Mask which was named a top toy for Christmas by Hamleys...