When are children not children?

A disturbing news story about two boys who tortured and murdered a two year old girl raises the question, when are children not children?
This isn't the first time that young children have committed such a crime, there is a similar case a few years ago in England where two boys took a younger boy and stoned him to death.

The conventional wisdom is that children are innocent and therefore unable to commit a crime. The law is structured in such a way that children under the age of 18 are immune from criminal conviction.

We must ask ourselves whether this is appropriate.
Is the justice system adequate to handle instances of children who are capable of committing murder without any sense of guilt or remorse?

Why do we make excuses for these under- age criminals?

What kind of adults do we expect these under- age criminals to become?
Model citizens?

Even if we remove the possibility that these under- age criminals are insane, we must consider the fact that people who are devoid of any emotion when it concerns the life of other human beings are in fact not fit to live within a society, are a danger to others within that society and do not and should not have the same rights as the rest of us.

Committing murder because of rage, jealousy or even by accident is considered by the legal system as extenuating circumstances that contribute to that incident.

Committing murder in cold blood doesn't have any redeeming feature or excuse to pardon the murderer. Including the under-age criminal.
A cold blooded murderer is simply that no matter what the age may be.

It's time to stop fooling ourselves that children are innocent and incapable of understanding the significance of their actions.