Translation:The Korean children are not playing by these trees, but by those.
In standard English, 'those' can be a pronoun as well as an adjective/determiner, so 'those ones' sounds odd to a native speaker educated in the standard language.
For me it depends on the rest of the sentence. If I use "these ones," I'll follow it with "those ones." If I say "these nouns," I tend to just use "those." For example: "I don't want these ones, i want those ones," versus "I climbed these trees, not those." Also, when you talk about being educated in "standard english," you may want to be more specific. British and American English have alot of differences. I don't know if it matters in this specific case, but can in others.
No, it should not have been accepted. In both English and Hungarian, near, next to and by are three different concepts.
Thank you - could you tell me how to express "near" in Hungarian? Much appreciated!