There should be a dictionary...

...that would answer the questions like "is there any language where...".

And since I don't have such a dictionary and have to ask my readers instead: every language that I know has the same word for child (in the sense of a person under a certain age) and child (in the sense of one's son or daughter). Are there any languages where these are two different words?

For that matter, are there languages that do not have a word for child (in the sense of one's son or daughter) at all, and only have words "son and "daughter"? (There are languages, for example Russian, that do not have a word for "sibling", only the words "brother" and "sister".) Are there languages that don't have a word for "parent" but only "father" and "mother"? Or the opposite: languages that have words "parent" and/or "child", but no separate words for "father", "mother", "son" and "daughter"? I think the latter is quite unlikely but you never know.

Why does the word "with" also mean "against" in so many languages? As in "fighting with X" meaning "fighting against X" and not "fighting against somebody else with X being on your side". I remember it being a sort of difficult concept when I was a kid.

"With" always meant "against" in English. The "together with", "alongside" and "by means of" meanings came later. I wonder why, and what happened to the preposition "mid" that used to carry all those meanings before that?

There should be some reverse etymological dictionary that would not show where the current words in a language come from, but where the extinct words have disappeared to.