Final answer:
The bird that sits in the old gum tree in the children's song is the Kookaburra, which is option c).
Step-by-step explanation:
In the children's song, the bird that "sits in the old gum tree" is c) Kookaburra. This Australian bird is known for its unique call, which sounds like echoing human laughter. Although the Bluejay is mentioned in your background information as a colorful and vocal bird, it is not the correct answer to the song reference.