If they meet the height requirement but they are under 7, they need to ride with an adult. My DD was 7 on our last trip, and if she wasn't riding with an adult right behind her, the CM would ask how old she was - this happened on Matterhorn and Splash when she rode in the front, then her brother (4) and then myself and DH. They always told us that we needed an adult behind the 4 year old.