The events that happen while he's confined to the room are hinted at, rather innocently from a childs understanding, but it's obvious what is happening, which i think makes it all the more harrowing.
The description off amazon...
Jack is five. He lives with his Ma. They live in a single, locked room. They don't have the key.
Jack and Ma are prisoners.
Room by Emma Donoghue is an extraordinarily powerful story of a mother and child kept in isolation, and the desire for, and price of, freedom.