J.
Great advice from some of these other moms who have already responded! Personally, I believe the whole concept of potty "training" is a myth....especially at
18 months!? It is great you are capitalizing on his interest and offering him tools (the kid size potty, encouragement, etc)but the whole learning experience needs to be owned by him. It needs to be his choice and his accomplishment! If the diapers are gone now, then he needs to learn for himself that poopie big boy pants are, well, poopie and no fun! I have heard of many parents who give rewards and/or stickers on a chart as the child has more success. (candy can be a great motivator!) Since stickers are a success with the peeing, try it, or the candy with the pooping too. You can't really reason with a 2-year-old, so let him figure it out for himself...I know this is easier said than done!
He is still very young, and obviously very smart and sensitive. My son was not out of diapers until he was on the verge of turning 3, and was not really totally reliable until 3+ and he was in daycare and had lots of good role models and 3 teachers giving encouragement!(the price of daycare was worth no potty hassles in our house!)
Interestingly enough, my DAUGHTER was pushing 4 before she decided she was interested enough to try the toilet on any regular basis. I casually put the mini potty in the bathroom with no fanfare when she was 2.5 and she ignored it for almost another year. She would pee in it out in the yard in the summer if we let her run around naked!! When she finally decided to get serious, she wanted nothing to do with the mini potty, she went straight to the big potty.... (she's really got a mind of her own, and I wanted nothing to do with it!) You will be able to look back and smile...promise!
Enjoy all this silly stuff, it makes for great stories later when they are teenagers. My oldest is 16, and we make him laugh, (and squirm) with all the goofy stuff he did.
Best of Luck to you guys and your little "Pooper"