Breathe. As much as I agree that kids have WAY too much control and the parents are more interested in being liked, rather than a parent, like the last post touched on, I don't think that this is where the discipline comes in - at least at this age.
Here's my experiences with 3 VERY different kids:
#1 - boy - almost totally potty trained at 18 months, then we left him with my parents for 2 weeks while we went to Spain. We returned and he refused to sit on the toilet for us. We understood it was him "punishing" us for leaving, even subconsciously. Fine, we got it. I tried discipline. I wouldn't put new batteries in toys until he sat ont he toliet - and THAT wasn't even demanding evacuation of his bowels or bladder! I even busted out the Oreo's and he told me to put them back into the pantry. Finally,we told him that on his 3rd birthday, there were no more diapers. When he woke up, we explained it again and took him out of them. He was mentally and physically ready - so his accidents that week made us leave the park since we can't play in wet clothes, etc. Literally by 7 days after he turned 3, he was 100% potty trained - no nighttime accidents - nothing.
#2 - boy - all of his motor developments are/were much slower than the first. We figured this was going to be a nightmere. Here's now almost 4 and we still have difficulty understanding some of his speech. But, he suddenly was potty trained at 2 years 4 months. Can't even really remember how it happened, but it did and it was MUCH easier than #1. He was ready. The onl;y time he wets his bed - every about 8-13 months is when his L2 is out of align,ent, so we get that adjusted and he's good to go -otherwise, he doesn't wake up to pee in the middle of the night.
#3 - girl - just turned 2 a few weeks ago. She'll pee on the toilet and we try to catch her for pooping as well....but not a ton of luck yet. It's frustrating, because she gets it. She'll tell us "I pooped," when she just pees and asks us to change her diaper. Her vocalulary is that of a 4 year old and she understands everything. We leave her undiapered a lot of the day, if we are home and take her to the toilet frequently....but once we put that diaper on, she poops in it. Ugggg. Really??? Her personality is VERY strong. She makes me look like a limp noodle and I am SO not. We are trying to find out what her currency is....and go with whatever motivates her. She does wake up many mornings with a dry diaper, so I KNOW she's physically ready for it.