Hi Rhonda,
A first trip to Walt Disney World! How exciting! With a 3 year old, I recommend concentrating on the Magic Kingdom, the crown jewel of the Walt Disney World Resort, and Disney's Hollywood Studios. Based on my experiences, a 3 year old would also enjoy Disney's Animal Kingdom and Epcot as well!
With regards to tickets, you are in luck! You do not have to know how many days you want to spend in the Magic Kingdom up front! Regular
Magic Your Way base tickets provide entrance to a single theme park on a given day. What you need to determine is how many days you would like to go into a theme park, not how many days for each particular theme park.
Since you said you are going for a week, you should consider getting a 7 day Magic Your Way ticket. There are two options you can get as well. The Park Hopper option allows you to visit more than one theme park on the same day; so for example you could go to the Magic Kingdom in the morning and Disney's Hollywood Studios in the afternoon. The Water Park Fun & More option allows you to add visits to DisneyQuest, Typhoon Lagoon, Blizzard Beach, etc. Since this is your first visit, I suggest not purchasing either option. You can always add them later while on your trip if you need to!
There are some great places to dine with a 3 year old. I highly recommend dining at
Chef Mickey's in the Contemporary Resort. My kids always love to eat with Mickey, Minnie, Donald, and other characters! As this is a very popular restaurant, be sure to make an Advanced Dining Reservation. Reservations can be made up to 180 days in advance! You can do it on-line
here.
Enjoy planning your magic vacation and write back if you have any more questions!