At what age are you pitching this explanation?
My take with my DC but not necessarily atheist - more open minded and trying to be respectful of beliefs, whilst not being a believer myself, is....
Throughout the ages, story telling has been used as an education tool. Through stories, we learn about consequences, respect, friendship, love and all the building blocks of society. The internet, even TV and to an extent accessible printed media to wider society are relatively modern things.
Religion is a form of society where people have a set of stories that form a part of their education and they feel represent the way they wish to conduct themselves. Stories are an easy way to remember lessons.
There are many useful stories that can be interpreted as relevant today from many of our countries religions. The Christmas story from the Christian book of stories - The Bible, is a classical one. We can take from it a time to stop and think about what we have and where we came from, to give and share what we have with those around us in need, family time. That anyone, no matter how lowly their birth, can rise and be a leader making a difference to the world - bringing people together who would previously have not connected.
Some people meet on a regular basis to reflect on these stories and learn from them, often called an act of worship. Sometimes this involves interpreting how the stories are relevant to us today and maybe even tweaking them to be relevant.
Stories that have been retold over the centuries have no doubt been slowly amended and made more fanciful to grasp the audience's attention.
Did these things actually happen, were the people in the stories real, are there any facts to back this up? Who knows. That's very personal and for each one of us to decide.
Does religion have a part to play in modern society? Absolutely. It's a strength for many people. It provides solidarity, support, community.
Overall individuals beliefs are deeply personal. No one person has the right to inflict their views on another be that in favour of a religion or questioning the validity of another's religious beliefs.
There's a great power we each hold in having self-confidence and belief in ourselves and our own convictions, something we see in many of the characters from the stories across the religions, no one has the ability to take that away from you unless you let them.