Simple! Don’t have Nickelodeon available to your young children, TV or internet. It markets to the t’ween down to infant age groups.  It’s much easier to control what the younger ones are exposed to.  By the time they’re fully into adolescence, little kids’ shows aren’t of interest.  
I’d have my kids living in a cave before I allowed Nickelodeon, Disney, or the like into my home.  If, perchance, my child did see something, at least he couldn’t blame me for it when he’s older.  
What’s the old saying?  You can’t stop birds from pooping while flying overhead, but you can stop them from nesting in your hair!