There are several things that could be affecting your son's behavior. My son took almost a year to potty train completely and we didn't start until he was 3. First, I notice that he has a younger sister. It could be an attention getter or a feeling that he still wants to be momma's baby. Although this may seem far-fetched to us, even the extra time and touch spent with a younger sibiling who needs it can affect the older one. Typically this behavior is coupled with other behaviors such as more temper tantrums or behavior issues at the dinner table. Secondly, structure is so important in a child's life, has anything changed with schedule, even something minor that could be throwing him off? Thirdly, has anything changed in his diet or activity level? My son would typically get so busy that he didn't realize he had to go until it was too late. Lastly, don't be too hard on him when he does have accidents (there is no indication that you are) but I know a little boy that was punished when he had an accident and then it became a vicious cycle, he would be scared and feel intimidated and would loose control and then would be punished again. Again, there is no indication whatsoever that this is your response, but I would correct/retrain without dwelling on the negative. It will feed the attention (if that is the root cause) or could continue the cycle.