Our two sons share a small bedroom ages 6, 10.
It’s incredibly stuffy smelling in the morning even with the air purifier running over night. Ife been opening the window in the morning while everyone is eating breakfast and closing it before we leave. My older daughter who’s a teenager cannot stand the smell of their room in the morning. It could be sweat and farts but it does have a terrible stuffy smell as I would describe it.
Would leaving a window with a screen open all night help?
Our home is setup like this here: