The constitutional rights of minors are (by and large) not subject to the whims of adults in society. Again, my copy of the Bill of Rights contains no age disclaimer. And if you read through the Constitution & Bill of Rights, age is only referenced twice (if I remember correctly) -- the age to vote and the age to be President. So it sounds like your real beef is with the Constitution.
Why should a minor have the right to be out in the middle of the night without an adult?
Uhh, because EVERYONE has (or should have) that right, so as long as they are not committing crimes.
Try letting your 2 yr old run around outdoors at night(or during the day for that matter) and see what happens.