For the safety of the riders, many attractions at Walt Disney World have height requirements. Epcot is no exception. Remember that the rules are set in place for your child's well being. It is not fair to your child, the other guests or the Disney cast members if you try to sneak your child onto a ride which he is she is not tall enough for. Trying to make the cast member feel guilty about disappointing your child is not going to make a difference. Your child can be measured before you get in line to make sure that there is no question about the height.
At Epcot there are three rides that have height requirements. None of the three are located within World Showcase. Guests who want to ride Soarin' must be at least 40 inches tall. The same is true for the updated version of Test Track, the height requirement is 40 inches. In order to ride Mission: SPACE the guest must be at least 44 inches. If someone in your party does not meet the height requirement for a ride ask about the Rider Switch option.