I'm not sure which specific 'baby reindeer original story' you are referring to. There could be many different stories about baby reindeer in various cultures and folklores. For example, in some Christmas - related stories, baby reindeer might be born in Santa's reindeer herd at the North Pole. They grow up learning to fly and help Santa deliver presents on Christmas Eve.
Since we don't know the exact 'baby reindeer original story', it could have the baby reindeer as the main character. Maybe its mother would also be an important character as she takes care of the baby. There could also be other reindeer in the herd like the father or the older siblings if it's a story that focuses on family relationships within the reindeer group.
If we consider a more general view, in some regions where reindeer are native, baby reindeer might be part of a herd managed by indigenous people. The cast (assuming you mean group) of baby reindeer would grow up learning from the older reindeer in the herd. They'd learn how to forage for lichens, which is a major part of their diet, and how to migrate to different areas depending on the season. Their real story could involve survival in harsh Arctic or sub - Arctic climates, dealing with snowstorms and limited food resources during the long winters.
I'm not entirely sure. It might be a real story if it's based on someone's actual encounter with a baby reindeer in the wild or on a reindeer farm. However, it could also be a fictional story made up for entertainment, like in children's books or movies where baby reindeer are often depicted in magical or anthropomorphic ways.