Barnaby Cork, from Thame, was struck by a car outside a sports centre on the town's Oxford Road shortly before 10:30 GMT on Saturday.
He died on his way to hospital.
In a statement, his family said: "We're truly devastated at the loss of our precious Barnaby. We're absolutely heartbroken."
They added:  "There's no words that can even begin to describe the sadness we're experiencing now that Barnaby isn't with us. He was our world."
Police have appealed for witnesses to the accident.
Barnaby's family added: "We are so very very lucky to have such close and strong family, as well as such great friends and neighbours, and your support means everything to us.
"We know the people of Thame have us in their thoughts and prayers and this gives us strength when we need it the most."
The family of a four-year-old boy who died after being knocked down by a car in Oxfordshire have said they are "absolutely heartbroken".