If Christians were truly brainwashed, then there wouldn't much of leaving the faith, but as I have seen here and in other places, there are a lot of people who have left the Christian faith for either a different faith or to no faith. (That point can be argued, I know. )
If Christianity and other religions brainwash people, then it can be said that anything a parent teaches can be called brainwashing. Is being taught to be polite (and to say please and thank you)a form of brainwashing? How about being told to wash your hands before you cook or eat? How about a father teaching his children about the basics of football or some other sport and watching and keeping up with favorite teams? And politics can be included to the list, too. In fact, school can be accused of brainwashing as well. Now, I am not saying that these things are brainwashing, I am saying that teaching of faith from parents to children isn't usually brainwashing either.