you're song

Last night as I was reading in bed, I heard our 9-year old singing from his room across the hall, so I got up to see why he was still awake so late (and to find out what he was singing, since I didn't quite catch what it was). He was lying in his cozy bed, all tucked in, softly snoring. He'd been singing in his sleep!
When I told him about it this morning, he laughed with delight, but he couldn't remember what song it was.