Thanks for bringing your question to the Moms Panel, Bita!
Having two children of different ages can sometimes pose a dilemma when deciding which attractions to ride at Walt Disney World.
Rider Switch allows two adult Guests to take turns waiting with little Mouseketeers who are unable (due to height restrictions) or don't want to ride a particular attraction. However, in your situation, it sounds like you'll be the only adult, so in that case, Rider Switch will not be an option.
Unfortunately, Cast Members are often so busy making magic for Guests, that they are unable to watch children. A dear friend of mine is a single mom with three young kids, and when she travels to Walt Disney World, there are some rides they are not able to go on. However, she was told by a Cast Member a couple of years ago that children are allowed to ride by themselves at age seven or older, so now that her daughter is ten years old she sometimes rides by herself while mom watches her younger brothers. Check at any Guest Relations window or ask an attractions Cast Member to see if this policy is still in place.
Also, check the Walt Disney World website for
attraction height requirements. I bet you'll find oodles of rides that would appeal to both of your kiddos. The Barnstormer at Magic Kingdom Park is an excellent beginner roller coaster that has a 35" height requirement. Slinky Dog Dash and Seven Dwarfs Mine Train have 38" requirements, and are two of the most popular attractions on property, delighting Guests of all ages.
Bita, I know you and your kids will have a vacation to remember this fall! Come back and visit us here at the Moms Panel if we can assist you with any other planning tips and tricks!
Eean