The boy, who has been locally identified as Peter Mulcaire and is believed to have lived in Abbeycourt, was involved in the incident yesterday afternoon.
The collision took place at around 3.50pm. The child sustained serious injuries and was brought to University Hospital Limerick by a member of his family.
Despite efforts to save him, he was later pronounced dead.
Gardaí have confirmed that the circumstances surrounding the incident are being investigated and that a post-mortem will be carried out.
The car involved failed to stop at the scene.
A man in his 30s was subsequently detained by Gardaí at a separate location on suspicion of driving under the influence of an intoxicant. He was taken to a Garda station and provided an evidential blood or urine sample before being released.
The sample will now be analysed as part of the investigation.
A family liaison officer has been appointed to assist Peter's relatives during the difficult time.
The incident has also had an impact across the wider local community. Sunday Masses in St Mary's Parish, Rathkeale, and elsewhere within the Diocese of Limerick were to include prayers for the young boy.
A planned family event at the Abbey grounds was cancelled following the tragedy.
Meanwhile, Gardaí are appealing for information from the public.
Investigators are particularly interested in hearing from motorists and other road users who were in the Abbey Court/Rathkeale area between 3.20pm and 4pm yesterday.
Anyone who may have captured footage on a dashcam, mobile phone or another camera is asked to get in touch.
Newcastle West Garda Station can be contacted on 069 20650. Information can also be passed on through the Garda Confidential Line at 1800 666 111 or at any Garda station.
The investigation remains ongoing.
