A Cartoon style can mean a lot of things, but some of the basic principles are:
Bold outlines
A low-resolution, simple style
Bright Colors on the scenery that contrast with the characters
You can do these with different ways,
a) You can create outlines by using slightly larger MeshParts that have flipped Normals to the mesh you are using,
b) Contrasting colors that are bright and fun, but remember to acknowledge the emotion your game is trying to convey
c) Low-resolution and Simple, this is where you want every part you insert to count, make the most out of your limitations.
EDIT By simple style I mean that the buildings aren’t generally complex in details and design. This isn’t an MC Escher house, this is a box with triangles for a roof.
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!