The first game I led in a meaningful capacity while I was at Disney was Disney Build It: Frozen. It's a premium builder game designed for kids based on the Frozen franchise. The imputus for the design was to create a a builder that didn't focus on free-to-play mechaincs or require resource managment. To that end, we designed a builder focused on creativity, but isnt' quite as open as something like Minecraft.
This was a project that technically started without me but my boss at the time tasked me with leading the design of this project instead of him. He left Disney partway through the games production, but he acted as an advisor when the game was being prototyped and designed.
Because Disney wasn't a developer, the game was externally developed by Nanu Interactive. However, we had daily calls with the developer and got near constant builds from them during the beginning of production, in order to properly iterator on our designs. The game had a pre-production period but the bulk of the game was designed in this back and forth process. I would provide build notes, write up detailed mechanic descriptions and draw diagrams to give the developer as much help as I could while the put together the game. I would also test the game on our end in both formal and informal playtests, taking notes on player behavior and writing up my thoughts on what could be improved on.