Auzou Book for my advent novel the mysterious reindeer

Elliot lives with his parents, who are reindeer breeders, on the edge of the forest. For Christmas, his cousin Flore comes to visit him. On their way back from the train station, they encounter a strange old man, a toy maker, who is searching for his lost animal. Back at the farm, they notice that one of the reindeer is behaving oddly... its coat shines remarkably, it almost looks like it’s flying! Could it be magical?