I had a little belly by about 9 weeks the second time. I was actually smaller overall though so it isn't a sign that you will be huge at the end, just that your ab muscles give up earlier.
This time around I had a belly at 6 weeks and now at 12 weeks I look like I did at 20 weeks the first time. Thank goodness I am far enough along to not try to hide it anymore.
Congrats on the pregnancy.