[necovek]

Let's stick to comparing language skills to language skills: at least in my experience with my two kids, they learn word formation patterns before they turn 2 — easy to notice because you see them make mistakes on exceptions.

LLMs needed how much training data to be able to do so?

FWIW, I still see them make up wrong words not following any grammatical pattern, esp in Serbian with less training data.

Serbian is pretty complex though: https://www.languagegrowth.com/en/blog/serbian-grammar-basic... — this made it even more surprising to see the kids pick them up so early when their vocabulary is probably not 2000 words yet.