We have been at both times. Would I prefer to go in Oct? Yes. But, with an older kid now, I don't want her to miss school anymore. So, off we went last August. Was it hot/humid/rainy? Oh yeah. But, no hotter or humid than we had left in NE!!! The rains were over the top, but I understand they were almost record breaking. The crowds were bigger than usual thanks to the FTP. The parks started closing a little earlier at the beginning of the third week. E-nights ended at the end of the third week.
If you aren't suffering with morning sickness, I would opt for the summer. Oct can still be pretty warm. It can be pretty uncomfortable 'wadddlin' around in the heat for long periods of time. Go to the parks early in the day. Drink a lot of water. Sit down for a brief rest every hour. Go back to your resort for lunch and a swim and a rest. Go back to the parks late afternoon for more touring or dinner. Most of all....relax and have a good time. WDW will be there for another visit with your little one. Don't try to do it all this one trip!!!