Any kid can dream up a roller coaster. But those who visit a new exhibit at Walt Disney World's Epcot theme park can actually take a ride on their fantasy creations. Epcot on Wednesday opened a new attraction called "Sum of All Thrills," which lets kids use computer tablets to design a virtual roller coaster, bobsled track or plane ride. After inputting their designs, kids climb into a robotic carriage that uses virtual-reality technology to help them experience the ride they've created.