I had two major obsessions as a child...
a) Horse-racing. I think I was around 9 when I started to have an interest in horse racing. It was also around the time when I started seriously reading the newspaper, because I saw my parents engage in that activity and I was wondering what the fuss was about. So, I started flipping through the horse racing section of the newspaper, which is located at the back of the sports section. My parents owned a fish and chips shop and two doors down was a deli, and the owner of the deli were friends with my parents and would give me the horse racing liftout every Friday. He would also talk about horse racing with me because he had an interest as well.
So, I'd basically spend all my spare time thinking about horse racing, watching the races on the TV, analysing the guide form and tipping, pouring over the results in the Sunday paper, etc. I would also go down to the local library and borrow books and videos about horse racing, and also about horses in general. There were some horses that I liked and would closely follow, and I would memorise their track record, breeding, owner, usual jockey, trainer, etc. I also knew the layouts of all the main Australian racetracks, and I had a fantasy racetrack with fantasy horses. I had notepads of fantasy horses, plus a fantasy racing calendar.
I was looking back through my written journals [I've kept them all] and it was funny to read in my first journal, I was writing about when <x> race was, who won it, what was their time, and then I'll talk about the rest of my day.
b) A certain Hong Kong actor. I think I was a little younger when I found out about him - maybe 8 - and I would insist on borrowing any movie with him in it. Didn't matter if he was a star or if he had a 30-second cameo - if he was in it, I needed to see it. Then, when I was home alone, I would grab the videos [yes, they were video cassettes] and would watch and re-watch scenes he was in. I'd pause, slow-mo, memorise his gestures, memorise his dialogue, memorise his facial expressions, and I would do that for hours on end.
My fascination with him lasted quite a while. I had a ball looking information up when I got online in '96, and once Google came, I had even more fun.
I also had an interest in dinosaurs, but I'm not entirely sure if that would be classified as a special interest. According to my mum though, she always remembered me talking constantly about dinosaurs. I remember there was one time when I was in grade 1 and I did a little self-project on a particular dinosaur and gave it to my teacher - it wasn't part of any official assignment, I just thought that she should know about this certain dinosaur. She gave it back to me and had the whole class give me a round of applause