Wearing cool hat like the kids (9)
I believe the answer is:
infantile
'like the kids' is the definition.
I can't judge whether this definition defines the answer.
'wearing cool hat' is the wordplay.
'wearing' becomes 'in' (you are 'in' the clothes you're wearing).
'cool' becomes 'fan' (fan can mean to cool down).
'hat' becomes 'tile' (old-fashioned term for a hat).
'in'+'fan'+'tile'='INFANTILE'
Can you help me to learn more?
(Other definitions for infantile that I've seen before include "for kids" , "Babyish" , "Inflate in childish way" , "in early stage of development" .)