Do you have a specific area of the world you'd like to know more about within the context of your question? Because for example fairly recently (within the 20 year rule) on 12th February 1993, a young toddler by the name of "James Bulger" was murdered in Liverpool, UK by two 10 year olds, Robert Thompson and Jon Venables.

What's interesting about this case above any other is the fact that the police investigators were shocked that two boys that were so young could commit such a crime. On 24th November 1993, Thompson and Venables were convicted making them the youngest murderers in English History. This case brought about changes in the UK's legislation, the biggest one was bringing the "age of criminal responsibility" to a set age of 10. Before this anything & everything regarding the "age of criminal responsibility" was ambiguous mainly because of the concept of "defence of infancy" (I'm not sure when this came into effect) which stated:

Under the English common law the defence of infancy was expressed as a set of presumptions. A child under the age of seven was presumed incapable of committing a crime.

The presumption was conclusive, prohibiting the prosecution from offering evidence that the child had the capacity to appreciate the nature and wrongfulness of what he had done. Children aged seven to fourteen (13 years, 364 days 23'59'59" aged) were presumed incapable of committing a crime but the presumption was rebuttable. The prosecution could overcome the presumption by proving that the child understood what he was doing and that it was wrong.

Children fourteen and older were presumed capable of committing a crime. However, the child could rebut this presumption by establishing that because of his immaturity he was incapable of understanding what he had done or the wrongfulness of his conduct.

So as you can see with this legal concept there was no clear line drawn in the sand as a clear of understanding for what they'd done even when we see faint glimmers of a line when it comes to the age of 14, the case can still be rebutted if the person in question can prove his immaturity in the sense that because of their young age, they had no idea what they'd truly done and the effect it would have.

This was all turned on its head pretty much with the Bulger case, because it was shown that the convicted knew what they were doing. However in a psychological context it begs the question that even if we are at the legal age for criminal responsibility, have our minds developed enough morally to understand the ramifications? That question can't be answered well generally and in my opinion can only be answered as best as humanly possible individually as the accused's history should be taken into account. E.g. With the Bulger case it was shown that Thompson and Venables watched Child's Play the night before.

So just because you're at the age of understanding and responsibility in the eyes of the law does that mean that one still can't be impressionable? It's seems that one can also be impressionable because in the Bulger case there were parallels between how Thompson and Venables killed James and that of how Chunky killed some of his victims in the film.

Psychologist, Lawerence Kohlberg says in his Stages of Moral Development: (his six stages were grouped into three levels; "Pre-conventional", "Conventional" and "Post-Conventional"), the level we're interested here is "Conventional" (stages 3 & 4):

The conventional level of moral reasoning is typical of adolescents and adults. To reason in a conventional way is to judge the morality of actions by comparing them to society's views and expectations.

Conventional morality is characterized by an acceptance of society's conventions concerning right and wrong. At this level an individual obeys rules and follows society's norms even when there are no consequences for obedience or disobedience. Adherence to rules and conventions is somewhat rigid, however, and a rule's appropriateness or fairness is seldom questioned.

So one can assume using Kohlberg's theory that the influence of Child's Play made such an impression (I'm sure there were other factors as well) on Thompson and Venables, that their Conventional Morality became so impaired that they wanted to re-enact what they saw. However their identities weren't released until after conviction & even then they were both given new identities due to the way in which Ralph Bulger understandably reacted upon release of their original identities

Hopefully I did answer your question and didn't digress too much :)

Further Reading and Sources:

1. David James Smith's The Sleep Of Reason: James Bulger Case

2. Lawerence Kohlberg ét al's Moral stages : a current formulation and a response to critics

3. "Age of Criminal Responsibility"

4. The concept of "defence of infancy"

5. JT Dalby's "Criminal liability in children".

6. Blake Morrison's As If

It depends on what age you consider childhood to have finished. Canon Law (Catholic) defines the age of seven years as "the age of reason" and children under seven as incapable of sin. Over seven years, children are considered to develop the ability to reason and sin but with reduced responsibility, depending on their increasing age, until they reach the age of puberty (under Roman Law 14 for boys and 12 for girls) at which time they are considered responsible for their own actions. At this age they may still suffer legal restraints/benefits about acts that are not in their interests.

See Catholic Encyclopedia, Discussion of "Minors"