Nap Optional?

Lately, I haven't really been pushing Ford to nap if he is keeping himself occupied. Some days he will sleep, some play with his toys or watch some tv. I just want him to know that he has to play by himself for a little while so that I can have quiet time. Today he played all afternoon while I worked, but as soon as I left for soccer practice he fell asleep on the couch watching Thomas the Train! What a sleepyhead - look at that hair!