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 ability girls and women have developed to hold several items at once in one hand. The skill has been developed due to the lack of pockets in women's clothing.
I thought she'd need multiple trips to carry her phone, keys, wallet, and Starbucks to her car since she needed the other hand to open the door, but she used her impressive girl grip to carry everything in one hand.