First off, I will say we were extremely lucky with DS. I had him sit on his little potty about once a month once he turned 2. While he was sitting there I would read book after book, just to get him used to sitting on it. We also read
The Potty Book for Boys frequently. He had no interest whatsoever in actually going on the potty.
Fast forward to the week before we leave for WDW (his first trip). DS is now 2y3m. He announces he wants to wear underwear. I told him that means you have to use the potty ALL the time. He says "OK". Now, I really don't want to start training him the week before vacation, so I told him we would look for big boy undies at WDW and when we came back we would start training (meanwhile I'm holding my breath that he doesn't change his mind in the next two weeks).
During the week we were at Disney, he used the potty at OKW about 3x a day (standing or being held on the seat). We searched everywhere for toddler undies but found nothing (they hadn't come out with the MMC undies yet or I would have packed them as a backup). The closest thing we found were boys size small undies at WoD (they probably won't fit him till he's 5 or 6). So be warned if you go looking for toddler undies at WDW!
Anyway, we returned home and put him in training undies the next day (thicker white cotton), but he didn't want to use his little potty. He wanted to use the regular one like mommy and daddy. So we held him on the seat until I could get out to get one of the seats that fits inside the regular toilet seat. And that was it. He was trained the minute he put undies on. He had a handful of accidents the first week, but that was it.
We used pull-ups at night only, but he was usually dry so we just switched him to undies for nighttime too. I will say that there was no way he was going back to diapers. His tushie was a little sore the one night and I told him we needed to put diaper cream on it. He had a huge meltdown (which was unusual for him) and we couldn't figure out why. Finally I asked him if he thought he was going to have to wear a diaper if he got diaper cream on, and he said yes. I felt so bad, so we had to explain it didn't mean he had to wear a diaper, and then he was fine.
BTW, I put the little potty in a garbage bag and stuck it in my trunk (with grocery bags for liners) so when we had to go out we could use the "travel potty" in an emergency. That is the only way he will use it. I truly think if I had made him use the little potty he would have been really resisted. So if you have a little potty, you might want to invest in the small toilet seat insert to have on hand.
Oh, and for long car rides/outings, I would put his undies on w/a pull-up over the top. That way he still felt like he needed to keep the undies dry, but there was a backup in case he couldn't.
Good luck everyone

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