I would think his underwear. A lot of young boys sleep in their underwear.
It is absolutely OK to sleep without pajamas or underwear. Nobody likes to feel restricted when they sleep.
All the guys in TH has said they sleep in their underwear.
Yes, it is ok to sleep without underwear because it may be more comfortable for some people and you're in the privacy of your bed.
You need to wear loose, cotton underwear and you can sleep on your back or side.
Girls should sleep in cotton to prevent infections.
Of course, you don't have to wear anything to go to sleep or to bed.
Depends on what's more comfortable.
It isn't necessary bad to wear underwear when you sleep, some people like the comfort of being totally nude and the feeling of the sheets agains they bodies.
I'm not sure why this is a problem, just sleep in your boxers. Tons of people sleep in their underwear or nothing at all.
Of course, unless your mom or dad says not to.
Because we want to, not all boys do.