The Giant's Son is the son of The Giant from "Jack and the Beanstalk."
The Giant's Son and his father were characters made real accidentally by the Ethereal Solidifier. He was playing around outside The Giant's Castle when he encountered Ecto-2, piloted by Winston Zeddemore and Peter Venkman. The son shot them with his water squirt-gun then took them into the castle to show to his father. The Giant decided he was going to eat Peter and Winston but let his son keep Ecto-2. Luckily, the Solidifier's effects were reversed and the son soon dematerialized.