The girl died on Thursday afternoon after two cars crashed into each other on the A94 Forfar Road.
It is understood that the two cars collided at the junction with Larghan Park then hit the children.
The girl's five-year-old brother and 17-year-old sister are being treated in Dundee's Ninewells Hospital.
The identity of the girl has not been released until formal identification has taken place.
It is understood the 23-year-old male driver of the Ford Focus and the 34-year-old driver of the Citroen vehicle involved in the incident were not injured.
The A94 was closed in both directions while police investigations were carried out.
Police have appealed for witnesses to the incident, which happened at about 15:20, to contact them.
Sgt Rory Fairbairn said: "We'll obviously be investigating the full circumstances of the collision to see how it came about.
"I'd also appeal for any witnesses that were in the location at the time that may have seen a black Ford Focus driving towards Forfar from the Coupar Angus area to contact us on 101.
"(Anyone) who may have been overtaken by the black Ford Focus as well, if they could contact us... and we'll speak to them."
The brother and sister of a two-year-old girl killed after being struck by a car in Coupar Angus remain in a serious condition in hospital.