The six-year-old boy knocked down by a car in Lisburn on Wednesday has died in hospital.
His twin brother was injured in the same incident but is reported to be in a stable condition on a main ward at the Royal Victoria Hospital.
The collision happened at 3.35pm on Railway Street in the city centre, close to on-going roadworks where two lanes merge into one.
The young boy died on Friday night.
The PSNI has issued an appeal for witnesses to contact Lisburn Police Station or the Collision Investigation Unit at Steeple Police Station on the non emergency number 101.
Lisburn Town North DUP Councillor Scott Carson said people were in shock following the tragedy.
“The events that unfolded in the centre of Lisburn on Wednesday came as a shock to many people throughout the city and many people across the community have been remembering the family involved,” said Mr Carson.
“Unfortunately a young life has been cut short following injuries sustained. Any death in such circumstances is difficult to come to terms with however it is even more tragic when the victim is a young child.
“I would like to express my condolences to the family who I can only imagine are heartbroken at this time.”
The Mayor of Lisburn City Council, Councillor Margaret Tolerton said the prayers of the community in Lisburn are with the boy’s family.
”My heart goes out to the child’s parents, twin brother and wider family circle.
“This is a desperate tragedy, and as a mother myself I can only imagine the pain and loss that is currently being endured.
“I wish to convey my sincere sympathies at this very difficult time and know the greater Lisburn community will be thinking of and praying for this family.”