Can a child suffer from retinal hemorrhage from falling off the sofa?

NO: Retinal hemmorhage requires high velocity back-and-forth motion. Simple impact, especially from the low height of a typical couch cushion to the floor wouldn't do it. There is an extensive scientific literature about this and some controversy about alternative explanations for the bleeding, all too detailed to summarize here.

Possible: It's theoretically possible, but unlikely unless there is direct trauma to the eye. If you have any concern that this is a possibility, head to the er.