The judge said that the experience of being locked in a windowless room in "appalling conditions" had taken a physical and psychological toll on the child victim.
Doctors who examined the boy said he was underweight and below average height for his age, and treated him for anaemia.
But Judge Norman Wright said that while the physical effects have been remedied, the psychological harm "will be unknown".
"It is bound, in my judgment, to be profound," he said.
More top news
A missile launched by North Korea has landed in Japanese waters, according to the Japanese Government.
A band of thundery rain moves northwards overnight.
The German chancellor warned the times in which the EU "can fully count on others are somewhat over" in the face of US divisions and Brexit.