Generally, I am the opposite. When they are old enough to be on a bed (I use crib mattresses) and out of the playpen (Around 2yrs) then I expect they are to come out of the sleep room when they wake up. This is hard for some of them, even till they're 4-5, but that is the rule. They come out and play quietly or look at books till nap is over.

When they are still in the playpen, I will use the particular needs of the child to determine if it's time to get up. If they are soo cranky... then its back to bed. Also, if they get up shortly after I leave the room then it's back to bed too cuz obviously they weren't asleep when I left.