Cartoony can be a difficult theme to accomplish, but some ideas that might help:
- Low-Poly
- Smooth Plastic(Think of like a childrens toy, it’s always shiny smooth plastic.)
- Warped and funky looking buildings or decor(For example, a building that tilts to the right.)
- Bright colors–pastel colors will work too
- If you were to add animals or humans–big eyes(Mickey Mouse for example)
- Themes that would be familiar to children
The important thing about replicating a cartoonish style is using references and inspiration from other games and media. Personally, I think a good reference for a cartoonish style is ToonTown. It has bright colors and funky characters, and the buildings are a good reference to use!
Hope this helps.