I accidentally made my daughter believe her uncle's brightly colored vegan cake was Play-doh and caused the entire family to do arts and crafts with it instead of eating it
What was the basis for your thinking? Did you not want to eat the cake?
It was fine the way it turned out.
This time it turned out harmless. But in the future you should be wary of lying to others even on accident.
I just wanted to make everyone learn about being kind to animals and being healthy by making all vegan.
Make believe can be fun sometimes but generally it can be bad to make people believe things that are not true.