Options for sound dampening for transfer vent

My spouse and I have a bedroom that shares a wall and air return with our child’s room. I’m looking to find something that will fit inside the air transfer that will dampen sound and reduce light between the rooms while still allowing airflow between them and to the air return. The options that I’ve seen tend to be primarily for transfers only rather than transfer + return.

Vents are 12”x6” with about 14” inside (vents are slightly offset. What options do I have, if any?