Meaning and origin of 子返し and 間引き

子返し

読み方：こがえし。

意味：

Return child.

間引き

読み方：まびき。

意味：

（１）thinning out; pruning; culling;

（例）ダイコンの間引きをする。

（２）〔間をあける〕Lengthen the interval．

（例）電車の間引き運転。

（３）infanticide

「子返し」 is a saying in the Edo period, that is, returning children, including parents killing children, abortions, and so on. Now it is more called 「間引き」. 

Return means returning to the gods. At that time, people thought that all children under the age of seven were children of God and could be returned to God at any time. 

Nowadays, 「水子（みずこ）」is often used to refer to abortion or aborted children.