Hi Victoria! I think it is great your children can join you while you attend a conference. They are going to LOVE Magic Kingdom and Hollywood Studios. I am a Cars fan, like your sons! Tow- Mater is just the cutest! You can meet Lightning McQueen and Mater at Disney's Hollywood Studios! You can also meet some of the well loved Pixar characters like Buzz Lightyear, and Sheriff Woody, just to name a few! You may also want to stop into Disney's Art of Animation resort and take a stroll through Radiator Springs! You can get some awesome pictures with some really cool Cars characters.
Your boys will adore Magic Kingdom, if you would like to reserve Disney Dining I suggest a reservation at the Crystal Palace restaurant. Given your sons ages, dining with Pooh and his friends may be just perfect! After a great meal be sure to check out some the classic rides including It's a Small World, Dumbo the Flying Elephant, and Peter Pan's Flight. Your younger boys may ride any attraction that does not have a height requirement. If your 4 year old is anything like mine, he may be tall enough and brave enough to ride Splash Mountain, and Big Thunder Mountain.
You may want to consider a day at Epcot! From March 5th to May 18th, the park will be in full bloom hosting the
Epcot International Flower and Garden Festival Presented by HGTV. My family loves seeing all the beautiful floral displays of Disney Characters. (You may even see some of the Cars characters in topiary form)
Enjoy your conference, and have a magical vacation!
~Jen