A fun way to explore what the early Christian community was like is to talk about graffiti! (Or graffito!)
There are wonderful images from catacombs, pottery, memorials, and more that feature early Christian symbols.
Some of these symbols are easy to recognize and others come from the Greek alphabet. For example, we sometimes write “Xmas” or “Xian” because “X” (or Chi) is used to represent “Christ” in the Greek alphabet! Chi-Rho are the first two letters of “Christ” in Greek.
If you search for early Christian graffiti you’ll find all sorts of marvellous images to share with your kids or try searching for paleochristian art/symbols). Try playing I-Spy with images from Catacombs or mosaics, or make your own paper mosaic with a favourite symbol. (For younger children you may want to provide a template for them to follow.)