A "wonderful" three-year-old boy who died almost a week after a crash on the M4 has been named as Jayden-Lee Lucas.
The boy's sister, four-year-old Gracie-Ann Wheaton, died in hospital a day after the crash near Newport.
The Tredegar family had been returning from a birthday party at around 1.45pm on Saturday February 5 when the car they were travelling in collided with a van.
Jayden and Gracie-Ann were rushed to the intensive care unit (ICU) of University Hospital of Wales in Cardiff.
Gracie-Ann suffered a cardiac arrest due to the severity of her injuries and died the following day at around 5am. Jayden died the following Friday at 4.30pm, his family confirmed.
Cousin Jamie Lucas, 19, from Abergavenny, told the PA news agency: "Unfortunately, after a week of fighting, Jayden has passed away.
"He was wonderful, creative and a kind soul. Turned the grey skies blue."
In a previous tribute to Gracie-Ann, he said: "I'm just trying to wrap my head around the fact that she's gone; it's hard to believe.
"She was so young. She had a bright future ahead of her. She was such a wonderful child.
"I'm just lost for words really. How she was returning from a birthday party and all of a sudden she's gone."
He added: "She was very smart, she was very creative. She had a really great imagination as well. She was just fantastic to be around."
A GoFundMe page set up to raise money for the siblings' funeral has reached more than £11,500.
The crash happened on the westbound carriageway between junctions 28 and 29, prompting a huge emergency services response.
The Ford Transit driver, 41-year-old Martin Newman, of Croeserw, appeared at Newport Magistrates' Court on February 7 charged with causing death by dangerous driving and two offences of causing serious injury by dangerous driving in relation to the accident.
He has been remanded into custody pending a hearing at Newport Crown Court on February 21.
Anyone with dashcam footage of the collision, or any information that could help the investigation, is asked to call Gwent Police on 101 and quote 2200041245.