With my first I used to do it all the time and I'm finding myself doing that now with both of my kids, especially if we've missed the window to come home to nap. Like today we drove home around 3pm and got stuck in traffic so I let them sleep in the car while I drove around, past our house, until they woke up. Usually takes us 35 minutes to get home. They don't normally sleep longer than an hour in the car anyway. Boy was I tired though! I wanted to nap myself. Kids have it so easy!