How free is "the land of the free" when several states and cities have installed curfew? [Details inside].

Last year my girlfriend and her parents were visted by family from America.
The two sons of this family told us about the existence in their city of curfew.
I had heard of that phenomenon; in the stories my grandfather told me about WWII.
We were flabbergasted we initially thought they were kidding with us about the fact that after a certain time (I forgot, but I believe it was nine-ish) they were not allowed to be outside.
How free is a country(/state/city) when it forces its adolescent citizens to be inside the house at nine?
Or am I missing an important issue/fact/reason here?