My parents have a layover in Charlotte. Can I go through security to meet them at one of the restaurants inside the airport if I am not flying?

To get through security, you need to present a boarding pass. There may be some alternate pass that you could obtain to permit you to enter. The easier option may be to have ypur parents exit and then return for the flight.

You definetly need a non-passenger pass to get through security.

I've never seen it done

Without a valid reason you can't get inside. You can ask your parents to come outside

Probably not. But if you have their reservation information, call the airline they are flying on and ask for a guest pass.