M2 gave up his nap around the time M3 came home. He just suddenly stopped falling asleep one day and I couldn't keep him in his room.
M.G. started having quiet time when she quit napping. She was pretty good about staying on her bed and looking at books or a quiet toy until "the hand pointed to" whatever number I told her.
In M2's case I couldn't get him to stay in his room long enough to even think about teaching him how to know when to come out. With the new baby it seemed like torture and easier to just let him be out with me.
But, Papa and I decided that in the long run it would be important to have the after lunch quiet time, especially seeing how it helped M.G. have a fresh start in the afternoons. She still has quiet time when she isn't in school.
M2 and I started with an egg timer and the goal of 15 min. of independent play in his room. He didn't have to be on his bed or even quiet, just in his room. At first it was mostly 15 min. of me taking deep breaths, leading him back, and trying to get him engaged in something. But, when the timer rang we were done trying for the day and could just move on.
Gradually he improved and after a few visits out to see me he'd play on his own for a good 20 min. He usually plays with a variety of things, but I always suggest some quiet things on his bed if he comes out. That rarely works, but then we just find something in there he is interested in.
One day he wanted to set the timer himself and cranked it to 40 minutes. He did come out a few times, but eventually sat down and played.
In the last month or so we've had good days and bad. Days where he didn't come out at all (and I kick myself for setting the timer for 35 minutes instead of 45) and two days where he ran out over and over until he threw a fit and actually fell asleep on the living room floor.
But twice now he's wanted me to put a huge pile of board books on his bed so that he can read. Today he stayed there, reading, the whole 45 minutes! When the timer rang he yelled, "My timer rang, but I am going to stay in here."
Amazing! 3 months ago I would not have believed it possible.