Is there any US Tax filling for people with double citizenship, but live in Japan from early childhood?

I am NOT an US Taxpayer, and I came here because this might be a common situation.

So I am a non-US foreign citizen living in Japan (PR) with my family. One of my kids was born in the US, and has a dual Japanese-US citizenship.
We left US when my kid was 1 yo., and have never returned after.

Are all American citizens automatically tax-residence in the US indefinitely? Does it mean my kid has to fill all the IRS paperworks and pay taxes to both country, if keeping both citizenship even if never return to the country?