How are we explaining religion/Christianity to our kids?

We are not a religious household. I would consider myself spiritual but I don’t adhere to any organized religion, although I grew up Catholic. As my son gets older and Christmas is coming — I’m starting to think about how I want to discuss religion and Jesus with him in an age appropriate way. He’s soon to be 3, and my goal isn’t to indoctrinate him to any specific belief system but also I don’t want the first time he hears about religion to come from someone else. I’d love to show him the beauty of all religions and cultures.

Have any of you been through this? How did you handle it?