At some point we started accepting 'little girls' for 'dziewczynki', as the word itself shows that the girls are quite young. And it works here.
Given the above, 'małe dziewczyny' is pretty weird, it would sound as older girls who have been miniaturized.
Why is "the little girls are wearing dresses" not accepted? Is there a different way to say "the girls wear" vs "the girls are wearing"?