Barnaby Cork was walking outside the Thame Leisure Centre on 10 December when he was knocked down by a car at 10:30 GMT.
Despite attempts to revive him, he died on his way to hospital.
The crash victim's family thanked the "amazing doctors" for their efforts and added they were "privileged to be able to call on the best support".
After the boy's passing, his father Stefan set up an online fundraising page to raise money for the Thames Valley Air Ambulance.
In under two weeks donations have exceeded £25,000.
Barnaby's father wrote: "Only this summer we were raising money for the air ambulance and never for one second thought that we would be calling on them in our own moment of need."
Chief executive of the Thames Valley Air Ambulance Amanda McLean said: "The thoughts of everyone at Thames Valley Air Ambulance are with Barnaby's family at this very difficult time.
"We are immensely grateful that they have chosen to ask people to support our work as one way of remembering Barnaby and overwhelmed by the generosity of those who have responded."
More than £25,000 has been raised for the air ambulance which treated a four-year-old boy who died in a car crash.