I believe anyone under 14 must have an adult as their riding buddy on any ride that only seats 2 (or 3) people. Think rides like: Toy Story Mania, Buzz, Peter Pan, Haunted Mansion, etc. And rides like Slinky or 7DMT, kiddos can sit with each other if a parent or someone older than 14 is sitting in the same car (like behind them). (Did that make sense?)
It's so hard on everyone - the cast members and others in line - if no one knows who is riding with who when you get up there. So tell the cast member the full number of people in your group - and they'll ensure you're kept together (for example, in Toy Story Midway Mania, it's 2 people per car, there are 2 sides to each car, and 2 full cars (for a total of 8 people) that go on a cycle together (and compete with each other for high score of the group!)
Rides that have bench seating - Pirates, Mickey & Minnie, etc. - the cast member knows best how to separate you if you aren't able to ride all together on one row - especially if some of the adults are larger.
If you aren't sure about ride configuration, All Ears has photos of ride vehicles
https://allears.net/walt-disney-wor...vehicle-and-attraction-seating-photo-gallery/