Twelve and 13 year olds who commit very serious crimes can now be referred to the Youth Court.
Until now, the Youth Court has dealt only with those aged from 14 to 16.
However from 1 October, 12 and 13 year olds who commit crimes such as aggravated robbery, arson and serious sexual assaults will now also be dealt with by the court.
The maximum jail term a Youth Court judge can impose has been doubled to six months.
The court can also now order offenders to attend parenting, mentoring or drug and alcohol rehabilitation programmes.
The changes are described as the biggest shake up for the youth justice system since its inception in 1989.
