Hi Jessica,
Please do not apologize for asking many questions! We on the Disney Parks Moms Panel love to help you to plan magical vacations.
I recommend that you go to Disney's Animal Kingdom on your half-day. Disney's Animal Kingdom typically has shorter hours that Disney's Hollywood Studios anyway, so you can stay at Disney's Hollywood Studios longer if you go there for your full day.
On a half-day at Disney's Animal Kingdom with children ages 5 and 2 years old, I suggest that you make it a priority to ride Kilimanjaro Safaris and see at least one show: either Festival of the Lion King or Finding Nemo - The Musical. Then, if you have time, your family might enjoy a ride on TriceraTop Spin, or heading out to Rafiki's Planet Watch for some up-close time with animals. I think that you can enjoy a lot of Disney's Animal Kingdom in half of a day.
I recommend a full day at Disney's Hollywood Studios with children ages 5 and 2. There is a lot for little ones at this theme park! They can enjoy Toy Story Midway Mania, Disney Junior - Live on Stage!, Beauty and the Beast - Live on Stage, and Muppet Vision 3D, among many other attractions. Your children might like to play on the Honey, I Shrunk the Kids Movie Set Adventure. Also, children that age may really enjoy the breakfast or lunch character meal
Disney Junior Play 'n Dine at Hollywood & Vine, where they can meet some of their favorite characters from Disney Junior.
I hope that this information helps you to make your decision, Jessica! Have a great time planning your trip, and please do not hesitate to ask if you have any further questions.