Before you travel to WDW with children you need to know 2 things.
1. How tall are all of your children?
2. What are the height restrictions on the attractions at WDW?
If you know these two things before you leave for your vacation, you can avoid many tears before they start! Don't talk about your favorite attractions if there is any chance your children may be too short to ride. You are only setting them up for disappointment.
WDWinfo has a great app on their web site where you can insert your child's height and it will show you which attractions they are too short to ride.
All Ears offers a great list of height restrictions and intense attractions for little ones.
Disney's Magical Beginnings offers a great print out for you to keep with you in the parks as a reminder of height restrictions. They also have additional information on traveling with little ones!