What is curfew?

A teenage curfew in something which parents put on their kids to restrict them from certain privileges, such as telling them to come at a certain time home, or to give them a sleeping time.

Teens need at least 8 hours of sleep, so it doesn't matter what time you give them a bed time curfew, as long as they have the amount of sleep.

Coming home at a certain time also depends on the area you live in. If it's a rough neighbourhood, the curfew should be earlier, and if it's a closed safe place, it could last later, or depending on what time you have dinner you can set a curfew.

Added: None of the above responses address the the fact that some municipalities (in the US) have enacted curfew LAWS which restrict persons of a certain age from either being out in public or from being in certain areas after a certain time of night. They usually draw complaints and occasionally court action from certain "civil rights" groups and are occasionally overturned, but many are drawn well enough and withstand court challenges.