Sorry, this is going to be long

. I wrote this to another dis-er right after we got back so I think I included every little detail. DD was 2 mos when we went.
We had a good time but it was definitely different than our other
Disney vacations. We have a really well-behaved and mellow baby so she was pretty easy the whole time. The real "issue" is that she's still eating every 2-3 hrs so that really slowed us down. We'd do about 2 rides and she'd be ready to eat again. I'm not sure about the crowds in Sept (the one time we went at the end of Sept, it was dead) but if it's busy you might be feeding him after every ride.
I'm nursing and my modesty (what little of it I had left after childbirth, lol) went out the window. They do have a baby care center in each park which was so great. DD got very over stimulated during the day with all the sights and noise and when she would eat, she wouldn't eat very much. We found that if we'd go to the baby center at least twice a day it would do wonders for her in terms of calming down, eating a full meal. It does take at least an hour though between travel time (there is only one per park and they're usually at the front of the park), feeding, changing. If you're formula feeding I would think it would be a big pita at the parks. Having to worry about bottles, mixing formula, cleaning bottles, etc. The other thing is my daughter likes to snack for lack of a better word. We had nursing problems at first and so I exclusively pumped. She would eat an ounce, want a break, then 30 min later want a little more. I don't think you can do that w/ formula, leaving it out after it's been started. Breast milk is fine at room temp for 4 hrs, but I think you have to discard formula after a short per of time. That would be a big concern for me.
If you are nursing, I would recommend buying a cheap hand pump. DD's feeding schedule got messed up, not eating as much/as often and I found myself engorged and it was great to be able to pump a little of it. It was also nice to have a bottle for the morning since after she was fed and we got ready and into the parks (about 2 hrs) she would be hungry again. This way MIL or FIL could feed her and DH and I could go on a ride or two. It was also great for the morning when we went to Chef Mickey breakfast so we could actually eat and she could too.
Changing is not a big deal. At first we would go to the bathroom and the baby changing station each time, pita. I would just lay down the changing pad on a bench and change her, much quicker.
Our little one is sleeping through the night, so that wasn't an issue for us. If she wasn't, I think that it would be hard to get up and go to the parks every day. We were still tired though and only stayed one night to see fireworks. We also took breaks some days and went back to the hotel for some calm time for baby.
The baby swap is great. You can bring on two other people with you after the first person rides. That way you don't have to ride alone. I don't think I'd want to go w/ a baby though w/out other people. MIL, FIL and niece 14 were such a big help. They enabled DH and I to ride some rides together which was really nice. I think having to ride every ride alone would take some of the fun out of it for me.
Also, get a baby carrier. I have a Moby Wrap and I love it. DD definitely got sick of sitting in her stroller for too long. I'm terrified of carrying her around Disney in my arms. People are rude, running and pushing through crowds sometimes and I was terrified of dropping her or getting bumped into. The Moby holds her so close that it feels to her like she's being held and leaves both of your hands free. It also is really great on the back. I can't recommend it enough.
Going w/ a little one is definitely possible, you just have to realize you're not going to be able to do everything you want and you're going to have to move slower than you normally do. It can be frustrating at times. DH really found that out when we wouldn't be able to wait in line or go to an attraction the rest of the family was because she needed to eat.
Sorry this is so long! If you have any other questions, feel free to ask! Congrats on your baby!!