Hello Heather! I am so excited to hear you will be visiting Walt Disney World for the first time. First time trips are so magical.
Buses start running 1 hour prior to park opening from the Walt Disney World Resorts. Because this is your first trip, I suggest getting on the bus as early as possible to get a good spot in line for the
Magic Kingdom Welcome Show. The show starts about 10 minutes before Magic Kingdom opens for the day. It is a fun little show with characters and dancers welcoming you to the Magic Kingdom. I recommend checking it out, it really puts you in a good mood for a great day at the park.
The bus will drop you off at the Magic Kingdom bus stop which is fairly close to the main entrance of Magic Kingdom. When you are ready to leave Magic Kingdom and head back to Disney's Art of Animation Resort, you will start walking to the same area that you arrived in to catch a bus back. When you are leaving, there will be boards with the names of the Resorts on it. That board is going to tell you the number of the bus stop you will need to stand at to get back to Disney's Art of Animation Resort.
I hope you and your family have the best time visiting Walt Disney World. If you have any other questions, please feel free to ask.