Zachary Barker, nine, died in hospital after the collision in Spring Gardens, Leek, in Staffordshire, last Saturday.
His mother Stephanie said she wanted others to "benefit from his short life".
She said transplants meant "even in death" he could carry on helping.
More updates on this story and others in Staffordshire
In a statement released by police, she said: "Zachary was just a lovely lad, full of life and joy. The whole family are devastated by the loss and we cannot believe that we will not see him again.
"He will remain in our hearts, thoughts and memories forever.
"We took the decision to allow his organs to be used for transplant, so that others may benefit from his short life.
"He was a tremendous son who was always willing to help everyone and even in death, he will continue to help others".
Police said a friend of the family has set up a Just Giving page to assist with the cost of the funeral.
The mother of a boy who died after being hit by a car says allowing her "tremendous" son's organs to be donated will let him "continue to help others".