Faster has hit the main point instantly...the kid(s) need their "own" space...no matter how small or inconvenient...when young ours relished the confinement and "fort" that was left by a PO of our house, where a duct crossed the closet space. I could get in by slithering on the floor, he had his bed space and toys...we did make him clean it up, standing by with dust cloth, polish and clean linens.
On the boat he loved the back of the quarter berth, even going so far as to use a foam board to "hatch" himself in. The quarter berth was storage, as it was too small for any real adult. This was on a Sabre 38. We did have a curtain.
As he got older, he did need some added space, and on our Ben 36CC he loved the vberth, it had a real door and then a partial door on the bulkhead, he could close both or just one as he needed. Again his space, we just encouraged cleaning and resorting on a regular basis.
Good prep for college dorm life, he respects and expects some privacy no matter how the space is laid out.