M.R.
I have gone through phases with both my boys of not wanting to nap. I just keep on putting them down and making them stay in bed. My now 5 yo can still take a 1.5+ hour nap, but rarely has time to sleep with Kinder schedule. My 3 yo, within the last year, also refused to nap. But I would tell him that if he didn't stay in bed quietly, I would take x aways (usually a toy he was into) and at least he staying in bed. After a while, he was back to napping!