Hi Patty,
There's so much magic awaiting you and your 2 children at Walt Disney World Resort. It's great that you're thinking ahead about what you'll enjoy.
One tip right off the start is to request a
Free Disney Parks Vacation Planning Video to get a fun, big picture view of all that's available to take in.
Looking at
Magic Kingdom Park, there are many attractions that can seat three of you together comfortably. I'm thinking of attractions with wide bench-style seating like Jungle Cruise, Mad Tea Party, Main Street Vehicles, Tomorrowland Transit Authority PeopleMover, Walt Disney World Railroad, Pirates of the Caribbean, and "it's a small world."
Attractions that typically seat 2-3 guests in the vehicle depending on size include The Magic Carpets of Aladdin, Big Thunder Mountain Railroad, Haunted Mansion, The Many Adventures of Winnie the Pooh, Peter Pan's Flight, and Under the Sea ~ Journey of The Little Mermaid.
Some attractions are better for 1-2 guests per vehicle like Astro Orbiter, The Barnstormer, Buzz Lightyear's Space Ranger Spin, Dumbo the Flying Elephant, Seven Dwarfs Mine Train, Space Mountain, Splash Mountain, Prince Charming Regal Carrousel, and Tomorrowland Speedway. You know your kids best. You might find that they'll enjoy these attractions even if the three of you are not seated three across. (Space Mountain might be the exception for you.)
Don't forget theater-style attractions like Country Bear Jamboree, The Hall of Presidents, Mickey's PhilharMagic, Monsters, Inc. Laugh Floor, Walt Disney's Carousel of Progress, and Walt Disney's Enchanted Tiki Room.
Keep in mind that Epcot, Disney's Hollywood Studios, and Disney's Animal Kingdom also offer attractions that the three of you can enjoy together.
Enjoy your Disney!
Jerry