Hi Lorelei!
You are going to really enjoy spending some Mommy-only time in Walt Disney World with your kids. I have done this on several occasions and treated it like "date-time" with Mom.
Unfortunately the "Rider Switch" program does require two adults to utilize. However you still have options for your older child to experience the thrill rides. First, as long as your older child meets the height requirements he/she will be allowed to ride alone since they are over 7 years old. You should accompany them in the line, but notify the Cast Member so that they can show you the "chicken exit" when it comes time to enter the ride.
Another option would be to utilize one of the childcare services at Walt Disney World for your 5 year old while you take your 8 year old out on a real date! A night riding all of the "mountains" followed by a turkey leg for dinner would make my 11 year old boy vacuum our house for a year. I have used the
Childcare services at Walt Disney World on several occasions and my kids loved them. In fact convincing them to come out of the kids club proved to be the challenge.
One tip for taking two children into the parks by yourself is to allow more time than normal. When one person needs to go to the bathroom you all will have to go. Also don't omit an attraction because you think it will be too "young" for your older child. If you tell the older child to "pretend to have fun" for their sibling, you will be surprised at how much they will enjoy the younger aged attractions. They just don't want to admit out loud they really loved the interactive queue at The Many Adventures of Winnie The Pooh.
Blessings,
Brenda ºOº