I never started the PC's in my world as beastfolk, but I did tend to give them abilities, qualities and even merge with creatures that eventually turned them into beastfolk.
One PC was 5th level I think and had a white tiger companion. During an encounter in a mages tower, they had a mysterious liquid spill all over them. Near the end of the battle, one in which they were losing badly, they only had 1 option and that was to retreat. Of course the only way out was to use the images teleportation mirror and when the PC made it to the other side he could not find his tiger. He finally noticed that his hands looked different and inspected himself only to find out that he was completely different. He and his tiger merged into one creating the first beastfolk in the campaign.