Hi Loubna:
I have a five-year-old and a three-year-old and have been traveling to Walt Disney World with them since they were infants. While we have fun at all of the four theme parks, the one park we never can go wrong with is Magic Kingdom.
While only a portion of the many Magic Kingdom attractions, our family always enjoys it's a small world, Jungle Cruise, Mickey's PhilharMagic, Peter Pan's Flight, The Many Adventures of Winnie the Pooh, Pirate's of the Caribbean, Tomorrowland Transit Authority People Mover, and Monster's, Inc. Laugh Floor. If you think your little ones would appreciate it, you can also check out Haunted Mansion.
Check out the
Magical Beginnings page for a map for tips and locations of rides and attractions suitable for kids five and under at all four Disney World theme parks.
Since it's a first visit, remember to check in at City Hall at the Magic Kingdom, or at guest relations at other parks, and pick up "first-visit" buttons. Many Cast Members will go out of their way to greet your family to make the visit more memorable.
Enjoy your vacation.