No Harem.
The Mc is reincarnated into a hidden Clan .The clan is exterminated due to its Kekkei genkai . The Mc creates his own village .
Not a child he gets reincarnated into a boy of 15 to 16
Timeliness is around 5 years ago from 2nd Shinobi war.
The Starting chapters may be a little bad to read but it has all improved in later chapters.