"Children, why are you bleeding?"
Translation:Kinder, warum blutet ihr?
Yes, I did that also. I think it is because one tends to use the familiar when talking to children or people close to you, and therefore Duo wants us to use du and ihr instead of Sie.
If the question had been "People, why are you bleeding?" then you would definitely have a correct answer if you used Sie.
Kinder, warum blutest du? would be wrong because Kinder is a plural noun, and du is singular. To make it correct, you either have to make the noun singular:
Kind, warum blutest du? -- Child, why are you bleeding
Or make the verb plural:
Kinder, warum blutet ihr. -- children, why are you bleeding.
This, and other sentences in this topic are always the same when I want to skip a level. I don't get harder material, they're always the same and I am on level 6.
It might he better to say "Kinder, wieso blutet ihr."
It seems to me that "warum" asks for a purpose, while "wieso" (literally "how so") asks for a cause.
"For what purpose did you make yourself bleed?" vs "What caused you to bleed?"
Is that remotely close to being right?
Ihr is the plural of du (it is also 'her' singular) [Thank you, German Language, for confusing us by using the same word to mean several different things]
Ich bin -- I am
Du bist -- you are (singular familiar -- to someone well known to you/friend/family member or a child)
Er/sie/es ist -- he/she/it is -- singular
Sie sind -- You are (plural/singular formal -- used for an adult you don't know well, or several of them)
Ihr seid -- you are (plural familiar -- used to speak with more than one person who is close, like family members or friends, or to speak with children)
sie sind -- they are.
So 'ihr' is used in this case as the plural familiar -- which you would use with multiple children.