ITA

. My 5yo watches those shows only because he catches them when my tweens are watching. When he watches Hannah Montana he walks around singing, when he watches Wizards of Waverly Place he gets an empty paper towel tube and pretends it's a magic wand and makes up his own spells to try to make stuff disappear. I do watch these shows with my kids often, maybe that's what makes the difference. They know TV is pretend, even the "real" shows.
My kids have spoken to me with attitude once or twice, but being punished by taking away video games or whatever their currency is depending on the child put a pretty abrupt stop to it. It sounds to me like these instances of kids copying TV are teachable moments, a chance for you to explain why they shouldn't repeat everything they see/hear on TV instead of taking it away. Then if it continues, punish them because they're disobeying. You're not going to be able to protect your child from seeing or hearing everything that you don't want repeated. My kids hear cussing on the school bus, that doesn't mean they're going to stop riding the bus. Model the behavior you want from them and talk, talk, talk.