Hi Jaime!
There are plenty of rides and attractions for all ages at Walt Disney World. The Magic Kingdom is my favorite park to take little ones. Even my 1 year old daughter has plenty of things to choose from to do. The easiest way to check out attractions is by looking at the
Attractions page of the Walt Disney World website. On the left, you can filter by height and location. This will populate all of the rides that are a certain height at a particular park or at all of the parks.
So if you choose 38" or under at the Magic Kingdom, you will find these attractions:
Haunted Mansion
Buzz Lightyear Space Ranger Spin
it's a small world
Dumbo the Flying Elephant
Astro Orbiter
The Barnstormer
Jungle Cruise
Liberty Square Riverboat
Mad Tea Party
The Many Adventures of Winnie the Pooh
Peter Pan's Flight
Pirates of the Caribbean
Prince Charming Regal Carousel
People Mover
Tomorrowland Speedway (with an adult)
Walt Disney Railroad
And these are just the rides! When you add in the shows, like Mickey's PhilharMagic and the Tiki Room, there are plenty of things for your children to do.
Have a magical day!
Leslie