So, every day on the way to Daycare, we drive past a church that has a giant cross in front of the building--It's bigger than the trees that surround it. Every day, my 4.5 year old son asks, "Momma, what's that?"
Me: "It's a cross, it means there's a church there."
Him: "Oh, what's a church?"
Me: "It's where people go to learn about Jesus." Change the subject.

(I was raised Catholic, but have been inside a church maybe twice in the past 10 years, and am not practicing any religion, so feel no need to get into religion with my kids at this point in their young lives.)

The next day:
Him: "Momma, what's that?"
Me: "It's a cross, it means there's a church there."
Him: "Oh, what's a church?"
Me: "It's where people go to learn about Jesus." Change the subject.

Lather. Rinse. Repeat. Every day.

Today he asks, "Why does the church have a cross?"
Me: "Well, it's kind of like there sign. You know, like McDonald's has the golden arches on their sign so you know it's McDonald's?"
Him: "Ooohhh. Okay."
Me: "Does that make sense?"
Him: "Yeah Momma, Church is like McDonald's."