In this question meaning of the
s' explained, but what if I'll say
my childrens toys (several kids), i.e. with no ' after s ?
The "correct" punctuation is "my children's toys" (=the toys of my children)
The toys of my child -> my child's toys
The toys of my children > my children's toys
The toys of my son -> my son's toys
The toys of my sons -> my sons' toys
The last two are pronounced the same. Note that apostrophes are frequently used incorrectly by native speakers, so we are likely to be more forgiving of people who write childrens'