Bumpy convertible

At the mall today, Amy and Michael made a beeline for the kiddie cars. My kids have NEVER seen any of the cars actually move. They just enjoy playing in and on them. Unfortunately for me, today, a grandmother was there with her grandchildren as well. She WAS putting coins in the machine to make them go. Amy and Michael watched in transfixed amazement. To my horrified surprise, the kind lady invited them to join her grandson on a kiddie school bus. The kids were beyond enraptured as the bus jerked up, down, and sideways. Once on solid ground again, Amy immediately ran toward a red convertible.
"Momma," She cried eagerly, "Can you make the 'verticle' go bump too?