Hi Michelle,
Taking your little ones to Magic Kingdom and Disney's Hollywood Studios will be so much fun! First, I suggest that you order the
free Disney World vacation planning DVD. If you watch it together with your children, you can start to see what really peaks their interest. I will give you some thoughts based on the ages of your children; however, there is so much to do at the Disney theme parks that you will also want to narrow it down based on their interests.
Magic Kingdom is truly a playground of magic for little ones. You can focus on Fantasyland, with wonderful attractions such as "it's a small world," Peter Pan's Flight, and Enchanted Tales with Belle. Depending on how tall your children are, and how much they like thrills, they might be ready for some more thrilling attractions. The Barnstormer is a very mild roller coaster, so you could start with that, and if they really like it, you can move on over to Big Thunder Mountain Railroad. At Disney's Hollywood Studios, be sure to check out Toy Story Midway Mania, a fabulous attraction that you play your way through. Also, if your children like the Disney Junior channel, go see Disney Junior - Live on Stage, where they can sing and dance along with a high-energy show featuring puppets of the Disney Junior characters. Finally, be sure to take in some of the amazing shows such a Beauty and the Beast - Live on Stage.
I suggest that you get to the theme parks as early as you can, even 30 minutes before the posted opening time. When you arrive earlier in the morning, the crowds are lower than they are later in the day, and you can enjoy many more attractions with shorter lines.
I would love to help you plan more Michelle; however, I am limited in how much space I have to answer. Please write back if you have any further questions!