the children weren't human children, the way hags make new hags is to eat human children. After they eat a child some hag magic lets them give birth to a new hag child that looks exactly like a human child until they hit 13 years of age.
they just "saved" a bunch of hag children that will turn into identical copies of the hags they killed.
they just "saved" a bunch of hag children that will turn into identical copies of the hags they killed.