T.C.
My son is almost 3 yrs old and we had the same problem with him. At first we thought is was because of so many changes but then soon realized it was something else. No matter what we did, take his toys away, make him change himself, etc. it didn't work. He kept saying he didn't like his pre-school and when he pooped his pant..which he never does, I paid attention. He know only has accidents every once in awhile. If he starts making a "habit" of it again, I take the toy away that he was playing with and remind him why I am doing that. This usually works. If he starts holding it too long, I gently remind him that I will take his toys away. This gets him back on the toilet. Oh, when I do have to take the toys away, I sit them outside his room, so he see's them and is reminded of why he cannot play with them. That has been the most effective method for me and one of my cousins who is a stay at home mom with 3 kids.