As had been said, going to church doesn't make a person a child of God any more than walking into a garage makes you a car. So what does a church do? What makes a church?
You've seen church buildings. Little white buildings with steeples on top, or modern stucco and brick structures with a naked cross on the front, or huge tall brick or stone things with lots of architectural detail. There are others. What's your favorite kind of church?
Churches are also collections of people. They may build a newer building or move to a different neighborhood. It's the same church-- same group of people, same church name.
There is also a church that has life, just like people have something called "life," of a different kind. This live church is not visible. In fact, even members of this live church can't tell for sure who else is in it! (or not!) But God, the Spirit who gives life, knows. All people who belong to God are his real "church."
Are you in?