The legal age of criminal responsibility has been raised from seven to 10 years old, and children up to the age of 12 will be exempt from criminal charge for all but the most serious crimes.
Minister of State for Children Brian Lenihan today announced the change would take place with immediate effect.
"The question of when a child should be held accountable for a crime is a complex one" Mr Lenihan said. "This legislation strikes the right balance between protecting young children who offend and protecting their victims and society as a whole from criminal behaviour."
The change was provided for in the Children Act 2001, as amended by the Criminal Justice Act 2006.
Children under the age of 12 can not be charged with an offence other than murder, manslaughter, rape and aggravated sexual assault.
As part of the new regime, prosecution for children the age of 14 can only take place with the consent of the Director of Public Prosecutions.
The new system means that when children under 12 are suspected of committing an offence they will be taken to their parents or guardians by a garda, and the Health Service Executive can intervene, through social workers or health care professionals, when required.
Mr Lenihan said further provisions would to be introduced soon for the participation of 10 and 11-year-olds in the Garda Diversion Programme.