I have never really been able to unscramble this verse so it makes complete sense. The quandary concerns that little two-word phrase (in Greek; in English it's three words) "in the Lord." Does it go with "obey" or with "parents"? It makes a difference.
If it means "obey in the Lord" then it is subtly saying there are times when disobedience is okay, when it goes against what the Lord says. But this has never been a big concern of Paul's elsewhere, so it doesn't really make sense in this context.
If it means "parents in the Lord" then obviously the next step is to try and suss out what that means. I confess I haven't a clue.
It appears that this little phrase was confusing enough that some scribes thought it was a mistake and left it out. Many old and important manuscripts don't have it; they just read "children, obey your parents because this is right." It's possible that some scribes added "in the Lord" later, but I don't see a good reason for anyone to do this because it just muddies up the passage. So I tentatively conclude that yes, Paul wrote it. Now, what the heck did he mean by it?
Thoughts?