What would you do if you were a 14-year-old kid who suddenly found themselves in the body of a grown-up superhero? Buy beer, right? And then use your totally awesome superpowers to beat up the bullies and save the world and stuff. The forthcoming Shazam! movie basically takes route one when it comes to childhood empowerment fantasies, and it looks like a lot of fun. It is such an obvious idea it’s amazing they didn’t think of it earlier (all right, they did: Shazam! was a 1970s TV series, and this movie has been in development for nearly 20 years).

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But if you really were a kid in the body of a grownup, might you also be curious to examine your new, mature body? And when you did, might you either be freaked out by it, or think of things to do with it beyond saving the world and buying beer? This is the elephant in the room when it comes to kids-as-adults movies, and there seems to be no appropriate way to deal with it.

We all know the wrong way to deal with it, which was Big. Yes, one of the first things Tom Hanks’s shocked manchild does is to peek down his underpants. But then he sleeps with grownup Elizabeth Perkins. That’s just weird. They part ways amicably for a happy ending, but Perkins’s character probably spends the rest of her life in therapy and on the sex offenders register. A similar thing happens in Jack: we see a 10-year-old with an accelerated ageing condition and Robin Williams’s body, although when he propositions his teacher, Jennifer Lopez, she knows where to draw the line. So Williams hits the bar and ends up snogging his friend’s mum, which is fine.

Then there is 13 Going on 30, where our prepubescent heroine wakes up in Jennifer Garner’s body, and must repel the hairy, naked boyfriend she finds in her shower – eeeuw! Later, she learns that her adult self has been having an affair. Again, a lot to process for a kid.

There is a similar tinge of wrongness around new Seth Rogen-produced comedy Good Boys. Its central trio are kids in kids’ bodies, but they are desperate to act like adults. Think Superbad with 12-year-olds. It’s an awkward age, to be sure, but we’d rather see that awkwardness put on to the movie characters, not us in the audience. The trick is to make it accessible to both kids and adults. A better tone was struck by Jumanji: Welcome to the Jungle, especially the character of Bethany, a teenage girl who finds herself in the body of 47-year-old Jack Black and in need of a pee. “Oh my God you guys, there’s, like, literally a penis attached to this body right now,” she/he says. So let’s see how Shazam! fares, although judging by the trailer, it conveniently confines its superhero within a tight-fitting costume, like a full-body prophylactic. “Superpowers?” he asks, “I don’t even know how to pee in this thing!”