The owner of a fairground in the southern suburb of Elliniko and the maintainer of the equipment used on site were handed six-year suspended sentences by a court in Athens on Friday over the death of a 13-year-old boy, and the serious injury of his 9-year-old sister in 2014.
The court changed the initial charges for homicide with possible intent and causing severe bodily harm to negligent manslaughter and injuries.
A third suspect, a foreign national who has absconded, was also found guilty of causing bodily harm from negligence and was handed a two-year suspended sentence.
Two more former fairground employees were cleared of any wrongdoing.
The boy was killed and his sister injured when a gust of wind blew a water roller on the site into the air.