It was confirmed. :]
The Deku Tree in WW is the Deku Tree Sprout from
OoT (the Deku Tree died, and after Adult Link broke the curse on the Forest Temple, the Sprout could grow on the AT).
He states the Koroks once took human shapes (the Kokiri are humanoid) and that they changed to adapt to life in the sea.
He even calls them his "beloved children" which is how the Deku Tree addresses the Kokiri.
The Kokiri are not children or Hylians. They are spirits of the Forest that are immortal and ageless that chose to take humanoid, elfin shape.
They're just spirits of the Forest.
tldr; Yes, the Koroks are Kokiri.