From what I've read, spirit animals are there to help you, and they will leave if you don't need their help anymore, but a new spirit animal will come. You will always have one. You should try contacting your spirit animal again, and it may not be the same one, but that would be a good thing because it would mean you learned what you needed from it :)
I don't know anyone else who met their spirit animal when they were so young, so I don't really know much as to why it came to you at such an early age. I can only guess that maybe its because you were really in tune with the spirit world when you were younger or maybe you just remember it when other people might not.