We switched M2 to training undies during the day and are still putting him in a diaper at night. We told him when the previous box of diapers ran out that we'd be out of daytime diapers. He asked if we should buy more and we said that he'd get to wear undies instead.
He's been doing really well. He had been using the potty now and then already and did pretty well the first day with potty breaks every so often. The first afternoon we were cooking something and he said, "What that on the floor under me? That water?" I told him what it was. He said, "That supposed to stay in my undies?" I explained how diapers and undies were different and responded with, "So I put my tinkle on the floor now?" Um, no.
The 2nd afternoon I think he was testing out the system - he managed to get 6 pairs of undies wet in about 2 hours.
But, yesterday and today he's been telling me when he needs to go and we've been taking bathroom breaks before snacks, meals, quiet time, and bed.
This afternoon he asked me if he was supposed to use the potty in the night. I told him he could wake me up and I'd help him, so we'll see what happens with that.
I think he's officially given up his nap now. I'm trying to teach him how to spend some time after lunch playing quietly in his room. We have an egg timer in there and each day he has been excited for me to wind it up. I'm aiming for 30 minutes right now. He'll play very well on his own for 15 minutes or so before wandering out. I bring him back and try to get him interested in a toy or book. He tends to run out a few times, but then each day has found something to keep himself happy for the last 5 minutes.
He's been a little tired without his nap, but has started falling asleep at 7:30 again, instead of 8:30 or 9.