Son of Rambow, 12A<br/>Awake, 15

You don't have to have been a 10-year-old in 1982 &ndash; or even a Stallone fan &ndash; to fall for this bittersweet nostalgic comedy

You know you're old when you start seeing films about the period of your own childhood, and they look as if they're set in a distant, enchanted era. I'm sad to report that it's happening to me. Last year there was This Is England, and now there's Son of Rambow, which takes place in an unnamed town in 1982 – although it could be decades earlier, as far as the 10-year-old Will Proudfoot (Bill Milner) is concerned. His family belongs to the Plymouth Brethren, a Christian sect which forbids access to cinema, television, records or radio, so Will even has to sit in the corridor when his teacher puts on a documentary about the wheel: "Man's greatest invention ... but the greatest bringer of death!"

Will's polar opposite, Lee Carter (Will Poulter) is a fast-talking cockney wide boy who doesn't just watch films, but sells pirate copies of them too. One afternoon, while blithely exploiting his innocent schoolmate, Lee exposes Will to his first ever movie: Sylvester Stallone's First Blood. Will, who's never witnessed such an orgy of gore and violence, is naturally delighted. Until now, he's had to vent his buzzing imagination by doodling multicoloured monsters all over his Bible, so he leaps at the chance of making a sequel to the Rambo film with Lee's video camera, and entering their mis-spelt masterpiece in the BBC's Screen Test competition.

It doesn't take the boys long to realise what they have in common. Will's dad has died, leaving his mum (Jessica Hynes) to raise the family by herself, as warmly as she can within the Plymouth Brethren's strict, sometimes sinister boundaries. Meanwhile, Lee Carter (to use his full name, as his admiring pal always does) has something missing from his home life. His parents live in Spain, so Lee is stuck in the care of a joy-riding big brother who expects to have his breakfast cooked. The boys find that they're kindred spirits. But even 10-year-olds can have creative differences, especially when their definition of what's cool is suddenly blown away by a French exchange student (Jules Sitruk) who gets his fashion sense from Adam Ant.

It's a risky business to make a film that wholly depends on child actors. Even the Harry Potter series has tripped up on their variable quality, so kudos to the casting agents who tracked down Son of Rambow's excellent double act. Poulter is a self-assured Artful Dodger with spot-on comic timing, Milner disappears into the role of an eager naïf, and the chemistry between them is perfect. Kudos, too, to Garth Jennings, the writer/director, for recognising that a film about children doesn't have to be childish. Son of Rambow derives from his own memories of attempting a youthful First Blood remake, so the film has all the offbeat authenticity of a true story as it looks back with nostalgic mockery at the pre-internet Eighties.

It's a Britain of endless meadows, and of classrooms where the sun is always shining through a window and turning the dust in the air into a golden haze. But it's also a Britain where cinemas are full of smokers, where mobile phones are big and stereos are bigger, and where a schoolboy's most prized possession is a rubber – or eraser, for our American readers – that "smells like real cake". It's a love letter to the days of Grange Hill circa Tucker Jenkins, and to Gregory's Girl, which was released in 1981, and which must have been on Jennings' DVD player constantly while he was preparing Son of Rambow.

At its best, his bittersweet comedy is as accurate and piercing as one of Rambo's arrows, which is why it's so frustrating when it veers off-target towards the end. Instead of telling us why Lee is so intent on getting on Screen Test, or exploring why some people might prefer a life of prayer to a life of running around a forest wearing a bandanna, Son of Rambow loses faith in its premise. It shoehorns in a car crash, a collapsing building, and a death-defying rescue – as if the story needed some real-life danger when it was doing so well with the boys' pretend adventures.

What's even stranger is that there's no explanation of who exactly the Plymouth Brethren are. For that matter, there's no explanation of what Screen Test is, which could be an obstacle for viewers who aren't of Jennings' (and my) generation. Much of the film's last half hour is too bitty to be involving, but even at its low points Son of Rambow still has the energy and individuality of a passion project. With the gleefully over-the-top jokes of a live-action Wallace and Gromit, and an uplifting ending which wins back the goodwill it squandered, it should bring a tear to the eye of most viewers, or most viewers who are a similar age to Jennings, anyway.

Another film by a British writer-director, Awake stars Hayden Christensen as the billionaire heir to a New York corporation – but he's one of those noble billionaires who are always "creating jobs and saving companies", as well as giving away a fortune to charity every year. No one could wish any harm on such a paragon, and certainly not his doe-eyed fiancée (Jessica Alba), his doting mother (Lena Olin) or his surgeon buddy (Terrence Howard). And yet, thanks to a faulty anaesthetic, Christensen remains conscious but paralysed while he's having a heart transplant, and he's sufficiently composed to work out that someone's trying to murder him.

For the first half of Awake, it's merely a bad film: dull, daft, and saddled with a leading man who acts as if he's under anaesthetic at the best of times. But if you stay awake long enough, it becomes a Bad Film, a juicy turkey stuffed with so many bonkers plot twists and so much dumb dialogue that it becomes weirdly tasty. You have to admit, there's a certain brilliant wrongness to the idea of a thriller hero who can't move a muscle.