I think I have weird kids. When DS12 was 3, he wanted to sleep in the PnP, so we let him.
Fast forward 8 years to when our youngest was 3.5 - even though he slept in a bed at home, he wanted to sleep in the PnP. I figured he'd try it and not like it and then he'd change his mind. Nope. He slept the whole week in the PnP. He had to sleep with his legs bent because he was too tall, but he didn't care. He slept well all week, and do did we!
And yes, the PnP is in the bathroom. We're terrible parents.