Hi Susan!
Whenever I hear a friend of mine is heading to Walt Disney World with little ones for the first time, I send them over
here to check out the resources on the right menu. I like to point out the park maps available in pdfs that highlight the attractions geared towards little ones. Also, there is a pdf with attraction height requirements for all the parks. This way, you can plan in advance which rides to skip over or plan to use Rider Switch tickets for.
You'll most likely find there is plenty to do with a little one. I've been with my own two little ones, and there is always more to do than can fit into a day. I like to take it easy and allow the kids to set the pace, so that it doesn't overwhelm them. I accept that I won't get to every attraction, but that just means we have something new to look forward to on our next trip!
Also, keep in mind the Baby Care Centers. I've used them for changing the little ones, taking breaks from the heat and feeding them, and even just to have a place to calm them down if I noticed they were overstimulated.
Of course, you have the Moms here on the Panel to help you with questions as you go along your planning. Please, let us know if you need help with something more specific so you are prepared for your upcoming trip. It's sure to be a memorable one for your family!