Hello Amy,
How exciting that you're planning your first Walt Disney World vacation! You're definitely in for a magical trip that you'll never forget!
Theme park tickets provide you with admission to 1 of the 4 theme parks -
Magic Kingdom,
Disney's Hollywood Studios,
Epcot and
Disney's Animal Kingdom Theme Park - for each day of your visit. With those base tickets, you're welcome to leave and reenter the same park as many times as you'd like in the same day. Leaving and reentering the same park won't use more than 1 day of your tickets, so no need to worry about that! When my kids were little, we'd usually hit the parks early and then head back for a nap after lunch so we'd be rested up and ready for some late-night fun back in the park.
If you're looking for more choices each day, you have a couple other options. You can add the Park Hopper Option to your tickets, which lets you visit as many of those 4 parks each day as you'd like. For example, you could start your day at Disney's Animal Kingdom Theme Park with a ride on Kilimanjaro Safaris and then head over to Epcot in the afternoon for dinner and Illuminations: Reflections of Earth. If the water parks and DisneyQuest Indoor Interactive Theme Park interest you, the Water Parks Fun & More Option might also be worth considering.
I hope that helps, Amy, and sending you lots of pixie dust with your planning! Please visit us here at the Disney Parks Moms Panel again if you have any other questions.
Beth