you would never say a prison was "little" in english, though! "small" is better.
Yes, totally agree. I realise this is the Dutch course, but for the benefit of people using this who are also learning English, Duo is giving a misleading impression of difference between 'small' and 'little.' I am not clear if there is a formal distinction about when to use either, but here goes my native English speaker perspective:
SMALL: appropriate in most circumstances, gives information about size, more of a factual / neutral tone than "little," can be used before or after noun. Examples: Her feet are small... The town I used to live in is small... The restaurant is too small for a wedding reception... Chihuahuas are very small dogs...
LITTLE: more nuanced, usually used before a noun, less factual regarding size and more about implying that the small size of something contributes to its charm. Examples: (e.g. about a new baby) "Oh! Look at her little feet!"... (or about a tourist destination ) "We went to a little town in the mountains."... "Do you remember that little restaurant by the beach?"... (or in a children's book) "The little, lost dog wandered through the dark, wintery streets..."
I really can't think that there would ever be good cause to describe a prison as "little."
Little also seems to lean more toward people or animals than things. My little sister, my little cousin, my little dog. Usually the exception is when something is nice (like you said, a little town). I just imagine someone going, "Oh, what a nice little prison." Lol
You could choose to convey the same tone as in "her little feet", to deliberately sound... belittling.
"You carry on running your crappy little prison and thinking you're a bigshot, but you'll always be a silly little man who gets kicks from controlling people. Why do you think I divorced you?"
Like OsoGegenHest says, I think "little" is essentially just like "small" except you say it when you want to make a point. "My dog had a bunch of little puppies," "That little hammer isn't going to get the job done," "This is a nice little setup you've got." Really you just say it to emphasize that the smallness is important.
"The prison is cute" would be a perfectly normal sentence by Duolingo standards.