Mustafa Ahmed, eight, died at the scene in Plumstead, after the collision as they headed to evening prayers at 7.30pm on February 19.
His father, Mohammed, remains in an induced coma and is unaware that his youngest son has died, friends of the family said.
He had a 10-hour operation on Friday and was facing more surgery on Tuesday.
Mustafa’s brother Ahmed, 10, suffered a ruptured liver in the collision but is out of intensive care.
Local Labour Councillor Asli Mohammed, one of the organisers and a family friend, told the Standard: “Mustafa was a happy, caring, compassionate young boy.
“He loved making everybody in the room laugh.
“His favourite thing was playing on the trampoline in his garden and loved football too. He was an outdoor child, he loved his outdoor play time.
“His mother Hayfa, she is completely broken, but the overwhelming support and kind words she has received from the public has been some comfort to her.
“I am not just a councillor but a friend of hers and her beautiful family.”
She added: “The family wish to have the privacy respected during this difficult period, their father has not even been given the news.”
Deputy Imam Sayed Kafil Ahmed told the Standard: “I was calling prayers when someone came in and said what happened.
“I went outside it was a mess.
“The boy used to come here for lessons, he was the perfect student. He listened and was so respectful. He was our best student. Normally kids don’t listen, he was different.”
The 20-year-old rider of the motorbike has since been arrested on suspicion of causing death by dangerous driving.
To support Mustafa’s family please visit this link.
Anyone with information that could assist police is asked to call 101 or tweet @MetCC and quote CAD 6036/19Feb.