Being totally honest right now, but I didn't know they existed, at least not in America. Then again, perhaps that's because I'm from New York City, arguably one of the most active, crazy places out there.
I can see why a person would want to place a curfew for kids, and quite honestly, if I thought it could work without flaws, I'd be all for it. I know way to many kids who get themselves into trouble for stupid stuff around the midnight hour. Placing a curfew would technically prevent stuff like that. But you have to remember who the curfew's being placed on: kids. The younger 10ish year olds, I can get, and a curfew probably would work on. But the old a child gets, he/she, by nature, tends to get more adventurous and rebellious. If a teen wants to go outside that late, and he's really determined, I'm sure he will. That being said, I feel a curfew could only get more and more kids into trouble. Also, I presume the parents of the kid would know that they're outside that late, so they (most likely) would be okay with it, unless the kid's sneaking out or is just disobeying his parents.
Also, where the curfew's being place would probably matter a lot, as well. If you placed a curfew in a more rural area, I feel people would be more likely to heed it. Note, I'm completely assuming here, as I've never lived in the countryside. If I'm being stereotypical, and it bothers you, I'm sorry. But I do feel that. Now if you were to try to place a curfew somewhere like where I live, in NYC, I'd just laugh. I can honestly say that with all the places to go to, all the attractions, a curfew would be a waste of time and money.
tl;dr: It's a good idea, and it could work, but I'm not for it.