The boy, locally named as Peter Mulcaire, is understood to have been from the Abbeycourt area of the town.
The incident happened shortly before 4pm yesterday, when the young boy was struck by a car close to his home.
A family member brought him to University Hospital Limerick for emergency medical treatment, but he later died from his injuries.
Gardaí have confirmed that a post-mortem examination will be carried out. A family liaison officer has also been assigned to provide support to Peter's family.
The vehicle involved in the collision left the scene.
A man in his 30s was later arrested at another location on suspicion of driving while under the influence of an intoxicant. He was brought to a Garda station in Limerick, where he provided a blood or urine sample for evidential purposes.
The man has since been released, pending analysis of the sample.
The road was closed while Garda Forensic Collision Investigators carried out a technical examination of the scene.
The tragedy has deeply affected the local community. Prayers for Peter were due to be offered at Sunday Masses throughout St Mary's Parish in Rathkeale and across the Diocese of Limerick.
A family fun day planned for the Abbey grounds was also cancelled as a mark of respect.
Organisers said the event had been called off following the "very tragic circumstances" in Rathkeale.
Gardaí are continuing to investigate and are asking anyone who may have witnessed the collision to come forward.
In particular, investigators want to hear from anyone who travelled through the Abbey Court and Rathkeale area between 3.20pm and 4pm yesterday.
Anyone who may have dashcam or other relevant camera footage is also being asked to contact Newcastle West Garda Station on 069 20650.
Information can alternatively be given to the Garda Confidential Line on 1800 666 111 or to any Garda station.
