Emergency services were called to the Exhibition Road and the New England Highway about 4.33pm after receiving reports of a vehicle and pedestrian incident.
Paramedics treated a boy at the scene, who was in a critical condition, but he died shortly after.
A woman in her 40s was also treated and taken to Rockhampton Hospital in a stable condition.
Queensland Police are investigating the incident.
“The Forensic Crash Unit is assisting Workplace Health and Safety with investigations following a fatal traffic incident at showgrounds in Wandal yesterday,” police said in a statement.
“A report will be prepared for the coroner following the death of a three-year-old child.”
The Rockhampton Show is due to be held on June 12-14.