"들판에서 뛰는 아이들"
Translation:Children running in the fields
Both forms are correct.
In English, this is one of the uses of the present participle. It can be used to shorten relative clauses in which the relative pronoun + verb (in present tenses) are simply replaced by the present participle of the verb
The children ||who run/are running|| in the fields
who run/are running, to be removed and replaced with "running" -->
The children running in the fields [...]
Agreed that this -ing form can be ambiguous at times; especially, when compound nouns are over-used with the hyphen between nouns being dropped out of pure carelessness.
E.g. The man || who eats || fish --> The man eating fish =/= The man-eating fish (Piranhas, sharks, etc) ...