3-month old baby to Disney World?! What to do?!?

I would highly recommend bringing your own stroller. One of those easy to fold up if she will fit in it otherwise I believe its $10 a day for a stroller to rent and I don't quite remember what they look like. You should definitely have hats for baby to cover her from the sun, short sleeves and dresses or shorts. Also take advantage of fast pass! Right when you get to a park map out what rides you definitely have to go on and head over to that ride to see if they have fast pass available. This is a ticket that is free that shows 2 different times on it and these times are when you can come back to the ride and bypass the line! Also there are "nursing" stations all throughout disney where mom can go to breastfeed if you still do, change diapers and just rest in an air conditioned enviorment with baby. If all the adults want to go on a ride I would also ask the employee at the ride about ride swap. This is where for example one adult stays out with baby and the other goes on the ride with the 4 year old and then the 4 year old gets to go again immediately with the other parent! Its really awesome! Also I would recommend checking out a website called allears.net its a great site for everything about the parks! I went in November and loved it!