"아이가 길에서 뜁니다."
Translation:The child jumps in the street.
For all who are confused about "에서": http://endic.naver.com/search.nhn?sLn=en&searchOption=all&query=%EC%97%90%EC%84%9C I think duolingo, at least in my experience with learning korean so far, is a good training tool, but still lacks a lot of content ppl should be taught. Use other websites aswell for comparison and additional guidance. And look stuff up if it's confusing, or outright not mentioned here on duolingo.
Because an action is going on there; "-e" means something is somewhere, but "-eseo" means something is going on somewhere. As far as I've understood. It's a lot like Japanese "ni" (existence in a place) versus "de" (action in a place). Plus, like Japanese particles, also "-eseo" means more than just one thing; with verbs of movement, it means "from". But pardon my limitations if I'm wrong (only Level 7 at the time of writing).
When I think about it, when i hear "jumping in the street" i think of the action more (jumping). I also think that depending on context, they could have moved to the street by jumping there from somewhere else (like the sidewalk). When i hear "jumping on the street" there's a nuance that the location has a significance (on the street specifically).