Just a small comment: I wrote "the animals' clothes" and it was indeed accepted, but it indicated that I was "almost correct" and the ideal answer should be "the animals clothes." As far as I am aware, the genitive apostrophe is not optional in English spelling rules (but maybe the rule has changed since I have been in grade school...?)
Well, in fact, they are not quite missing. We initially thought we might be missing some from the translations, but they are there. However, for some reason, they are not 'identified'. While everything is fine with the apostrophe being followed by s in a word (for example, girl's), there seems to be a problem with 'identifying' the apostrophe at the end of the word, after the -s. We are not sure why that is exactly, but we are hoping to fix this on the new tree! ^.^
Just for information, in English, when you have an irregular plural such as "children" which is clearly the plural of "child", the apostrophe on the genitive plural goes before the "s": children's. Also "women's" and "men's", etc.
(When I started secondary school, we were clearly told that we were at the Girls' High School, not "Girl's", since there was more than one girl attending the school and "girls" is a regular plural.)