There are many reasons why curfews exist. We have curfews here and they never effect my children. Why? Because neither of my children are out and about during the times that the curfew is in effect. I don't know about in other states, but here the curfews don't start at a decent hour. During the school year and school day it starts at 11:00 pm and ends at 6:00am. During the weekend it starts at Midnight. Children should not be out and about during those hours.
My question would be, why do you feel it is necessary or okay for children to be walking the street at One O'clock in the morning?
Police only approaching youths deemed to be participating in " threatening" behaviour will lead to many problems for them. Why? Because its profiling. What one officer deems threatening, the next may not, and we would all be silly to think race wouldn't play into that. Not just for black people, but all ethnic groups, which ones would depend on where a person lives. It's asking for trouble. Saying all youths under 17 cannot be out during a certain time limits/prevents that.
Now in my state, there are exceptions, older teens may be coming home from work or on their way to work ( am hrs) and as long as they have proof of that they are not in violation. That's a legit reason to be out after curfew.
In my area children travel far via metro to schools all over, so leaving early is a must. If they are on their way to school (am) they are not in violation of curfew.
Last exception, if you are with a parent, you are fine, but even then you are usually on a legit commute.
I get what you are saying, but the bottom line children, do not need to be hanging out in the streets during the middle of the night. I don't know any child/youth who takes midnight walks to look at the moon. Night photography is cool and some of the best nature photos needs to be taken early in the morning before traffic and before sunrise sometimes. Yes, youths can be into photography, but would you really let your say 15 year go out by themselves to take those pictures? You would probably be with them and they would not be in violation. ( In my area, can't speak for others)
Aside for the reasons listed I don't know any legit reason for a child to be out all night and those that are, are up to no good. Curfews are needed and I like them.
ETA: Was curious so I checked out your previous questions. Do you dislike any law that dictates what parents must do? Or are you a student, playing devils advocate, perhaps?