Well the only problem is that YOU will notice changes far sooner than anyone else because you know how you look - so to the average person there's doubtfully much change. As for showing sooner, you earlier than 12 weeks there's nothing there to show. Baby is too small to cause any form of actual belly - bloating and retention cause most of your weight gain appearance early on.
The reason you show sooner is that the muscles in your stomach are much looser than the first go around, due to previously stretching once already.
I dont know if its normal or not but I felt like I showed quicker with my second and now my 3rd. I am only 8 weeks pregnant and I feel like I look 4 months!!!