Imagination and function or type

There are various functions that are tied closely to imaginative thinking.
The most common being Ni and Ne. Lately, I have read that Fi and Fe are very closely tied to imagination.
It all has me wondering who is imaginative and why?

Another observation: only children despite type seem to be relatively imaginative.
Lastly, ISTjs I know tend to get frustrated with my many "what if" scenarios and don't like imaginative conversations.

Share any ideas!
Thanks.