[hrktb]

We’d have to look closer to the study, but there is a lot of research reaching the conclusion that learning languages has lasting effect on the brain, in particular in bi-lingual children ([0] for instance)

In that respect, picking back a language they once developed the “hardware” to fully master would be faster for them than people starting from scratch, even if presumably they’ve completely forgotten it.

I’d also expect children having learned language with the same structure to learn Korean faster, just as fully bi-lingual people learn tjeir third or fourth language faster in general.

[0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6124684/