Congrats to all the expectant mommys. Now I suppose exercising caution is always wise, however, my doctor told me that for the first trimester or so, the baby is so small that the pelvic bone cavity really is protecting baby from any injury. She even said skiing was fine! While it makes sense to avoid anything that will make you more queasy, I can't think of anything at WDW (mayve ToT) that would be harmful that early in the pregnancy. Of course, check with your own doctor.
Most important, have fun. Don't forget to figure in swollen feet if you are farther along and exhaustion that often comes with the first and third trimesters. Drink water and rest and you will be fine.