The presumption that children between 10 and 13 cannot tell right from wrong is often overturned now.
The most notable case involved the two 10-year-old boys who were convicted of murdering the Liverpool toddler James Bulger in 1993.
But the same applies to scores of less serious cases which are brought before the youth courts up and down the country.
However, switching the burden of proof from prosecution to defence would reinforce in the minds of sentencers that children ought to be exposed to the full force of the criminal law at an earlier age - and much younger than in most comparable countries in Western Europe.
It would signal an end to the view that young children should not be held as fully criminally responsible as adults, even though the civil law already provides for those out of control to be made the subject of supervision or care orders, or where their behaviour is particularly serious, secure accommodation orders.
The change would mean an end to the prosecution being required to produce something more than proof that an offence has been committed.
In serious Crown Court cases before juries, this typically takes the form of testimony from child behavioural specialists and/or a child's teachers.
In the more run-of-the-mill cases before magistrates, it will usually be evidence of the way that the child responded to police questioning.
If it was implemented, Mr Straw's proposal would put Britain out of line with the practice of other European Union countries.
BRITAIN OUT OF STEP
t Germany treats 14- to 18-year-olds as juveniles and 18- to 21-year-olds as adults