I took 8 year old son Sean to see this on Sunday. He enjoyed it. I was expecting the very worst having looked at some of the YouTube Fred stuff, and also read the one- or zero-star ratings in reviews. I wouldn't say I was pleasantly surprised, but it wasn't as inane as the mysteriously popular web videos.
Fred is meant to be a 15 year old in the plot, but plays like a much younger person, emotionally he is infantile. It's hard to see how any teenager would sit through it as it requires some serious suspension of disbelief, though the basic plot is of unrequited teen love (with happy ending).
It does, however, deal with bullying and isolation, very much from the point of view of the victim - the credulous and often stupid Fred. If it wasn't for the annoying voice, you'd have to have a flint heart not to feel sorry for Fred and hope he escapes his isolated social torment.
The happy ending is achieved, and largely deserved, by Fred's own hitherto unsuspected talent for creating imaginative YouTube videos - one of a few self-referential passages. Having said that, I wouldn't describe the script as arch, knowing or ironic to any great extent, though the imaginary scenes were so seamless that Sean (8, remember) didn't always get them).
Fred acts in a one dimensional manner - that's pretty much the whole point of the character, loathe it or hate it. But there are some supporting performances of genuine quality.
On the blood and swearing scales it is nowhere near 12A. More like U. There was nothing truly violent or gross. Mostly cartoonish slapstick. Some mildly funny. Sean laughed sometimes.
Possibly the most inappropriate part of the film for the sub-12s is that a successful party is seen as one in which teenagers get very drunk and throw up. But my main warning is: if you find Fred's voice irritating on a short YouTube clip (there's even a wee sketch in the movie about just how irritating the voice is), you'll have to arm your ears to get through an hour and a half.
On the plus side, it shows public transport, and bus drivers especially, in a very good light - unusual in the movies, but normal in everyday life. That, at least, was refreshing :-)
It cost us £14.40 - adult & kid, no concession. Maybe not worth it on balance - Sean enjoyed it and seems to have been unharmed but I think we might miss Fred 2.