Hi Claudia,
Thanks for visiting the Disney Parks Moms Panel with your question. I am happy to help you figure out the best
Walt Disney World theme park tickets for your traveling party.
It sounds to me like what you need are three-day base tickets. These will allow you admission into one of the four Walt Disney World theme parks (Magic Kingdom, Epcot, Disney's Hollywood Studios, or Disney's Animal Kingdom) each day. If you only plan to visit one park each day - which it sounds like you do - then the base ticket is the way to go. With base tickets, you can visit any combination of the theme parks, just no more than one on a given day. You could spend three days at one theme park, or go to a different theme park each day. If you think that you would like to go from theme park to theme park on any given day, then you will need to add the Park Hopper option to your tickets.
For your family, it sounds like you will need to purchase four adult tickets and one child ticket. This assumes the child is between 3 and 9 years old. Anyone 10 and up is considered an adult in purchasing tickets for Disney theme parks, and anyone who is not yet 3 is free.
I hope that this information is helpful for you, Claudia! Have a great time planning your trip, and please do not hesitate to ask if you have any further questions.