"He was a really brave four-year-old," Drum said.
"When we got there he was sitting on the swing."
Westpac crew were at the scene for about 20 to 30 minutes.
The boy's father went in the helicopter, while his mother drove to Starship Hospital.
Drum said the young boy went into surgery soon after arriving at Starship.
Paramedics did not remove the stick at the scene, Drum said.
"You have to be a little bit careful as there are important, main, blood vessels in the lower groin area.
"There is a chance it could be blocking something from bleeding."
Drum said he believed the stick was about 800mm long.
"Anything longer would have to be cut in half to make it easier to move him around."
St John ambulance and fire crew emergency response also attended.
Drum said "[St Johns paramedics] were really helpful with moving him around and keeping him calm."
Starship said the boy remained in hospital this afternoon in a stable condition.