How do you guys deal with your child if he or she starts making friends with the naughty or more troublesome kids in school?

Keep an eye on your child. Remember, you can't just impose on him that he shouldn't be friends with these naughty kids. It will keep him wondering why and might lead to curiosity. The least you can do is to guard your own child's behavior that he doesn't adapt the behavior of the other kids. I believe that when a child has a strong foundation at home, he can't be easily swayed by other people's behavior.