Translation:The children who are in the hospital are not happy.
That would be the translation of: Çocuklar hastanede mutlu değiller. And that doesn't exactly mean the same. It sounds like children aren't happy to be in the hospital. If they were elsewhere, they'd be happier.
The original sentence has no such hint. It just says that thr children are unhappy, and they happen to be in the hospital. We don't know if they're unhappy because of that.
I propose "The hospitalised children are not happy" as an alternative to the current translation. The introduction to this unit presented "-ki" to turn a noun into an adjective. Here, the English version is using a subordinate clause instead of an adjective (or may be not - my English is not native).
The children who are in the hospital -- patients The children who are at the hospital -- visiting I don't speak American English, so I don't know if these prepositions have the same functions for Americans.
Is there any difference when writing Turkish? Both in and at are accepted as correct answers.
Why, "the children form the hospital are not happy "is wrong
If you wrote this, "form" then Duo did not recognise the word.
It's like the children are bricks, being used as building blocks.
Sorry, just being stupid.
Try your answer again;
"The children from the hospital are not happy."
Please reply if Duo accepts or declines your answer.
Just so I know.
+++Thank for your reply
Why was your answer declined?
I suppose that, "in" means they are patients & "from" could mean, visitors?
Hastane + -de + -ki
So the locative suffix reinforced with the possessive suffix means, in or at the hospital only.
Please try, "at" the hospital because we already know that, "in" is accepted.
I will try, "at" during a practise lesson too.
Thank you very much & you're welcome.