I tell him, "It's time for nap, pick two books".
I find him with his "two" books.
I start to say, "Now, that's more than two. Let's look and pick out just two. Which ones do you like the best?"
But then, I think to myself, what's the hurry? We have no where to be this afternoon. So what if nap is delayed by 10-15 minutes? Is the schedule more important than "us" time?
Suddenly, his vision of "two books" is much more attractive than mine.
He went down for his nap a bit later. Best decision of the day.