Although I had preoccupations with things before that, I would say that my first obsession was with the little sister of a playmate. I was 6 and I wished she was my sister. It lasted the year I was 6.
My second obsession started when I was still 9, but for the most part when I was 10, and 3rd when I was 11, with my 4th obsession starting when I was 11 going on 12, starting with interest soon turned into an obsession, which lasted way into my teens.
Throughout my teen years I had obsessions with TMNT.
I had interests as a child, like reading, writing, children's shows and games that had nothing to do with obsessions or special interests.
I always liked animals, dinosaurs and cars, trains and other means of transport, but I think they were more like interests than special interests.
I always cared about animals and have always felt very strongly about animal rights and welfare, and conservation of endangered species, but I don't think that constitute a special interest, it's a value, a cause I believe in.
When I was 6-8 I was very into seals, I guess they were my special interest at the time. I think my special interest in dogs started at around 8.
My turtle special interest started when I was about 14, but I have always liked turtles, always thought they were cute.