Hi, Kari! What a wonderful idea to take your little princess to Disney World! My two youngest had their first vacations ever at Walt Disney World, and I have so many priceless memories of the experience!
September is usually a great time in terms of crowds and cost. Because most schools are just back in session, you'll find the theme park crowds typically lower in September than at other times during the year. For the best bang for your buck, consider one of the value resorts. There are several options - including three All Star resorts and Pop Century. The rooms are nicely themed, and the resorts all have great food courts, themed swimming pools, and free transportation around Walt Disney World.
You might also be lucky and find there are other promotions going on to make the trip more affordable. Walt Disney World has offered free dining plans during off peak times, as well as other promotions. Keep an eye out at
www.disneyworld.com to check for any special offers.
The only drawback to September is the heat and humidity. It can be quite warm during the month of September. If you plan to dress lightly, keep everyone well hydrated, and alternate between indoor and outdoor attractions, you should be fine.
Have a wonderful vacation with your baby girl!