I keep getting similar words mixed up.
for example kaniwani says Father (Papa) so I immediately assume 父 since Papa is colloquial/casual but the answer expected is お父さん. Same goes with Mother.
Don’t get me started on the multiple words for girl, boy, woman, man.
Any good solution?
Same here. On kamesame though I press undo and if it is word i knew i pressed it in if not mark it wrong.
You can add synonyms on KaniWani in the settings
Add the Kanji where “Word” is, and the kana where “Reading” is
In case of 父, if anything, it’s less casual than お父さん.
When using polite language you’d refer to your parents as 父 and 母.
slightly off topic I guess, but aren’t 父／母 more formal than お父さん／お母さん?
edit: ha, ninjad by @d-hermit
This happens to me all the time. I use KameSame sometimes but it just doesn’t feel the same as KaniWani.
I try to remember how it describes the word, for example, 男の人 is described as “expression” while just 男 does not have “expression”. Same for boy or so
Oh yeah. I was completely getting them backwards as to which was more formal! I was applying silly logic that the longer word must be more formal (笑)
You can also add synonyms here on WK, and they’ll show up there as well. So you can add things like “the short one” for 父, and “the long one” for お父さん 
That’s brilliant, I had no idea that WaniKani could cross reference like that - thanks for the amazing tip! For a newbie like me that’s some amazing info 
that’s a great idea!
It’s not exactly about formal here. They’re both the same amount of formality, but one is humble and the other is honorific.
父 is used most often when speaking to someone about your father, i.e. in a humble way. You wouldn’t often use this with friends, but with strangers you likely would.
お父さん is honorific in that you’d almost always call your father this directly. It’s somewhat situational when speaking with others.
The “less formal” way of saying father would be something like パパ
It’s not a question of which one is more formal. It has to do with humble and honorific language.
When speaking to your father, you should use お父さん because it is an honorific term.
When speaking about the father of the person you’re talking too, you should also use お父さん.
But when talking about your father to other people, you should use 父 because it is a humble term.
However that only applies in formal language. When speaking casually, you can use お父さん to refer to your father.
