The 4-year-old was killed in a crash on the Monaro Highway near Mugga Lane on Saturday, devastating a young family that has remembered Blake as an intelligent and inquisitive boy who would have had a bright future.

Blake's aunty, Christine Heard, said he was a delight to play with, especially when he brought out his toy trains.

"He knew them all by heart and had many wonderful adventures pushing them along the tracks," she said.

"He also loved puzzles, and could complete jigsaws that were well above his age group.

"He kept his parents on their toes because he was always on the go, and they loved him for it.

"When Blake walked into a room, everyone’s energy levels shot up in the most beautiful way."

Ms Heard said the family was beyond devastated by Blake's death, but thankful for the support of the emergency services and everyone who had helped them in the past few days as they tried to come to terms with the tragedy.

"As Blake’s extended family, we are receiving immense comfort from knowing that his parents and brother loved him so well, so perfectly," she said.

"We will all continue to love him."

Blake was travelling with his parents, who suffered minor injuries, and 2-year-old brother, who was not injured, when the crash happened about 9.30am on Saturday.

Three cars and a truck were involved, with six people taken to hospital for treatment and the highway closed to northbound traffic at Hume for about eight hours.

On Monday afternoon, an ACT Policing spokesperson said the cause of the crash remained under investigation.

It was the seventh fatal crash on ACT roads this year.