Potty time

Ever since Christmas, we had been doing potty training with our boys. "D" was really good in the beginning, when he needed to go, he would tell us, and we would take him to the potty.... it doesn't matter if it is no.1 or no.2... "A" didn't want to go at first, but now he is getting much better... whatever they want to do, they have to go potty first. However, "D" kinda take a step backward... he doesn't want to go now... any idea how i can make him tell me when he has to go again? but they are doing much better than i thought.