Eight-year-old Bartek Plachta, from Poland, was a back-seat passenger in a Ford Focus involved in the collision on the A92 in Kirkcaldy, Fife, on Monday.
The child died at the scene and driver Monika Lewandowska-Ritchie, from Durham, was taken to hospital where the 36-year-old died the following day.
A boy aged nine, also in the back seat of the car, suffered serious facial injuries in the crash just before 3pm.
The relationship between the casualties was not made clear by police.
The Polish boy’s family said in a statement: “Bartek was a much-loved and treasured son and brother.
“He was a very popular boy who touched the hearts of many and will be sadly missed by everyone who knew and cared for him.”
Ms Lewandowska-Ritchie’s relatives said: “Monika was a loving wife, mother, sister and daughter who was much-loved and will be sadly missed by all who knew and cared for her.”
A 36-year-old man travelling in the front of the Ford Focus escaped uninjured and the Iveco lorry driver and his passenger were not hurt.
Police have appealed for witnesses to the incident just north of the Redhouse roundabout, which closed the route for seven hours.
Inspector Brenda Sinclair said: “Our sympathies are with the families of Bartek and Monika, and we will continue to provide them with all the necessary support and they assistance they require.
“Fife road policing unit has been conducting a thorough investigation into the full circumstances surrounding this tragic incident and we remain keen to speak to any motorists who were on the
A92 at around 2.55 pm on Monday and witnessed the collision.
“In addition, anyone with any further information that can assist with our inquiries should also get in touch.”
Anyone with information is asked to contact Police Scotland on 101.
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