I still find it a little hard to believe that at some point in their 10 years they wouldn't have been introduced to the concept of killing another person being a bad thing whether it was from their parents, school, other adults they were in contact with, their own contemporaries, even television or film. But, if it were the case, then I'd have to say that they'd had an incredibly bleak existence.
Your final sentence accurately summarises the life of far too many children in the UK. Low class job, minimal prospects, bad parenting that many of us realise made them do crap at school, meaning they haven't had the preparation required to ever seriously educate themselves to specialise in a business sector, result: crap quality of life that they see is their future, so escapism through any adult pursuits with the 'wrong group of friends' is what happens.
Look at the rubbish some children are fed, the lack of parental attention - children lumped on a sofa to watch tv, or left alone outside to do whatever they want with friends, often on rough estates that are mostly council owned. All these small factors link together to morph a child into having a statistically small chance of ever achieving much in life, which is why from a young age many end up in all sorts. Peer pressure and social manipulation with multiple people participating can drive children to do all manner of horrible things, as with cases we have seen recently.
My own opinion is that the UK is not a very good place to live anymore or be brought up in as a growing child, and I certainly don't plan on having children in the distant future.
In response to some other comments, children and certain groups of people possess an inability to look at 'the bigger picture', or take a look at situations from an outside perspective.
Children do not just 'become' killers or abusers, just as adult paedophiles do not simply generally decide to grow a sexual attraction to children. Severe psychological issues - which does not excuse any of the adult actions - are seen to be the cause.
I really am against criminalising children through beurocracy, and although obviously certain children do very appalling things, it seems unfair to label them with a badge if they have only done something based on a rather messed up past. Can a child be held responsible for the bad, negative and socially damaging, upbringing by attrocious parents or guardians? I believe not. Can they, when they are adults, having had the chance to face their problems - liek an adult should - be held responsible through councilling or therapy? Most definitely yes. Some people will never have self awareness or realise they are crazy. Those people can pose serious issues to society, and they should be treated as the adults they are.
Children do not have this ability, as they learn it over many years. Rushing them into growing up can lead them to a whole host of other problems, such as humping each other and getting pregnant aged 12, boozing, and everything else on the list.