I think 18 months was probably a bit young to start, however I had an 18 month old boy that wanted to go on the potty. Basically, we went when we took him, but didn't if I didn't take him. I didn't actually consider this potty training. When he gets older, it will "click" and he'll tell you when he wants to go. I can say with my last son, he started around 2-1/2 and now, at 3, tells me when he needs to go and has VERY few accidents (maybe once a month). So, just stick with it. As for sitting or standing, my older son started sitting on the potty backwards - grandma swore by this tecnique and taught 4 boys to potty train. Younger son, stood from day 1. I think it's whatever they are comfortable doing. My opinion, if he'll stand, that's the easiest and cleanest way (he doesn't have to touch the toilet) if he stands. Next thought, pull ups. Older son was in diapers through that 18 month on up time until I was really ready to potty train (remember, I didn't consider that potty training). Once he was training, just undies, no pull ups (unless for nap or bed). Younger son started at 2-1/2 and went straight to undies. I think this helps them realize when they have to go and to start to control it. I also did a lot of naked time. Something about being naked from the waist down made my younger son not have accidents. We also allowed him to go in the yard, which was fun and novel for him. Another idea for you, keep a water bottle with a lid in the car for those inpromptu times when he has to go and it's not easy to unload and go inside (I have 3, so it's a LOT easier if I don't have to take everyone in for the 1 to potty). I can get that one child out of the carseat, put his weenie in the hole of the water bottle, he can pee, and we can be on our way. Just make sure you don't mistake it for apple juice! Ha, ha!