"Napping" lasts until at least 3, or until the child can't/won't fall asleep anymore.
But everyone has a quiet time. Usually, I will put the babies down first. This gives the bigger kids time for lunch to settle, and they can do something that isn't allowed out with the littlest ones roaming. (Right now, the Barbie dress up is a big hit. Those tiny shoes just cannot come out with the one year olds around!!)
Then I get them to lay down on the couch or whatever. Lights out, curtains closed. We have recently taken to putting on a Dora video or some such thing. I don't mind, as it is the only time we have the TV on.