Solutions:
A: Stop talking to your parents. (This is my personal favorite)
B: Show them the opening scenes from something like Elfen Lied or Crimson Climax. (The former if you don't want to end up in a mental hospital)
C: Should you not want your parents to ban anime from the house entirely, as Plan B could have them do, get them hooked on Shin-chan. It's got plenty of semi-clean adult oriented episodes, so they'll never need to move on to any other show, which would force them to realise most anime is childish.