"The small Japanese trees are pretty."
Translation:A kicsi japán fák szépek.
Both should be accepted here.
Other than that, here are the differences:
"Kis" can be used in compound words:
- kislány - litle girl
- "kisfiú - little boy
"Kis" can only stand in front of a noun, not behind. Consequently it can only be singular.
- kis fa
- kicsi fa
- kis fák
- kicsi fák
The tree is small:
- a fa kicsi (not possible with "kis")
The trees are small:
- a fák kicsik (not possible with "kis")