My two cents on night training
Basic caveat -- this is only my experience, but it's based on training two kids and I thought I would share. I know there is a lot of debate about when and how diapers should be taken away at night and how proactive the parent's role should be in nighttime potty training. I now firmly believe that kids can and will night train on their own, and that the potential risks of actively night training do not outweigh the potential benefits.
My oldest day trained at 19 months. She wasn't really showing too many "readiness signs" but we went cold-turkey to underwear for awake time (kept a pull-up for naps and night). She did well, it took about 2 weeks but we kept her in the pull-up for sleep because it was always SOAKED. A couple of different times, she asked to sleep in underwear and each time we let her. At about 27 months we tried actively night training by waking her up at 10 pm and 3 am (we tweaked the times a lot). Out of about 3 weeks of doing this, we got maybe 3 perfectly dry nights, and on two separate occasions she woke up asking to pee on her own. Not a great success, in my opinion, and it set us into a very long stretch of frequent night waking and bedtime problems. Maybe not related, but in any case, as we tried to recover from that, we were not about to do anything at all that interfered with consecutive hours of sleep. We went back to the pull-ups.
Then we started day training our little one. She was 17 months and we didn't do total cold-turkey because she had nursery school some days and she was very young, but shortly enough we were in just underwear. Unlike her sister, the little one started waking up dry from every nap (we ditched the nap pull-up after about 3 days), and even some nights (at 18 months). We tried underwear for bed, but she usually has about 3 consecutive dry nights followed by a wet night, so we continued with the pull-ups for bed and were just happy to reuse them a few nights in a row.
We started letting our big girl choose at naptime whether she would do underwear or pull-up. She started more and more choosing underwear (we didn't mind the clean-up so much when it wasn't 3am) and woke up wet almost every day for a week. Then she started asking for pull-ups again. One day, several weeks later, the nap pull-up was dry. THe next days he chose underwear, and has every day since, and has been dry every day since! About two weeks later, she had her first dry morning ever! A week after that, another dry morning! And now, a month after her first dry morning, and 2 weeks before her third birthday (almost 18 months after day training!), she is waking up dry about 3 nights out of 4, just like her baby sister.
This is the girl who was so soaked every morning just 6 weeks ago that if she did not wear a nighttime pull-up or diaper, she would soak through. We had no reason whatsoever to believe she was anywhere near being able to do this, and then all the sudden she did! And the fact that her little sister can do it already just shows me how different their bladder capacities are, particularly while they're unconscious. For each of my daughters, I'm going to wait for a full weeks of dry nights and then get these pull-ups out of the house!
I just wanted to offer this because when I was trying to figure out what to do with my girls, I anguished a little over what my role should be. I was afraid I wasn't doing enough to help my older daughter, and then when I did try to do something, it felt like it ruined EVERYTHING! I'm so glad she came around on her own, when her body was ready.
I feel like the night time thing is so different from daytime training, when "readiness" is certainly a factor, but does not mean what a lot of people take it to mean. (Basically, a child ready to train him or herself with little to no accidents). So my advice is: don't stress over night training. It will come, and it could come at 18 months or 3 years or I'm sure even later than that!