A word similar to childish, used to define someone who acts
like a kid in most cases. However it does not have to mean
immature but simply acting
like someone of a young age, or showing something that relates to a kid.
Examples:
My girlfriend wanted me to go to the playground with her then go
back to her place and
eat cookies and milk to me that just seems kiddish.
The
toy aisle at walmart is very kiddish