I have a five year old with DS, Delaney, and her three year old sister, Mckenna. Delaney just turned five last week, but she still isn't potty trained. There are always exceptions, but most DS kids don't get trained until five or six due to developmental and physical delays. The best thing to do is to make it a routine, as much as possible, and continue to use the younger one as a good influence. A reward of some time seems to work well - we do a small thing for "trying" and a bigger thing for potty successes. If she goes to school, make sure that they are doing a potty routine at school too. Also, books and videos on pottying seem to be somewhat helpful. I'd love to talk more through email if you want - ____@____.com.