"We run to those trees, from which the children run away."
Translation:Azokhoz a fákhoz futunk, amelyektől a gyerekek elfutnak.
By separating the verb from the prefix here, you imply that the children are running away from the tree right now. I don't know if present continuous would be absolutely necessary in the English sentence if this is the meaning. If not, then your sentence is correct as well.
Also, "amelyikektől" is actually incorrect in Duo's sentence, it must be "amelyektől", as you wrote.
Thanks again! I keep seeing "amelyikek + case ending" in a lot of these exercises...
OK, I just wrote in another comment that "amelyikek" is the more correct version, only too complicated, hence the usage of "amelyek" instead. :) At least that is what my logic says. But I am OK with saying that it is even incorrect. Is it actually, officially incorrect?
What is the difference between amelyek and amelyikek, between for instance amelyikektől and amelyektől. we see alternatively both forms in the solutions. What is the plural of melyik ? mely, melyek, melyik ? The solutions are not clear with that, either.