I personally spent a lot of time playing video games, watching TV, and riding my bicycle to see friends. What about you all?
I spent a lot of time watching cartoons and playing N64 (Banjo-Kazooie, The Legend of Zelda: Ocarina of Time/ Majora's Mask - and Mario games with friends) I loved making people laugh, loved telling stories and inventing worlds, writing stories and talking to myself/ being alone.
I liked to play with Legos when I was younger. I used to build houses and sometimes I would try to create mini towns with my legos. I would use an old milk carton as a milk factory.
Play with Hot Wheels. Set up scenes straight from my imaginations and re-inact some action shots right in my head. During the outdoors, I would collect some ladybugs and lay them on my hand and closely observe them--then let them free; what was interesting about this was when they would deploy their per-flight wings and make them stick out from their shells. This would be the most fascinating thing I observed when studying ladybugs when I was like five.
Computers. Playing games, trying to fumble in ignorance with the Internet (back when it was very basic), learning every crook and ridge of Windows. Also play with Hot Wheels, disassemble everything I could find when I got to my father's toolbox, and making my little sister laugh.
I still play games, I am now extremely knowledgeable of the Internet, and I know Windows 98, XP, 7, 8.1 all throughout and have an advanced knowledge of Debian-based linux systems. To top it off, my sister and I laugh harder than ever now that SHE knows Internet. No hotwheels, though, and screwdrivers only on my computer.
One of my best friends growing up was obsessed with cars and mechanics (and is now a mechanic/classic car restorer) and we spent a lot of time tinkering with engines, rebuilding lawn mowers, tuning up field motorbikes, etc. It was great fun and I still look back very fondly on it -- I guess not so many people can say they've completely taken a car engine to bits and put it back together! Another friends was a massive scaletrix (slot car) fan, and had a great track in his garage, and we spent many hours there shooting-the-shit and racing slot cars. When I was younger, it was definitely riding my bicycle around and exploring the countryside -- make tree houses and "bases" and running around all day exploring. Great fun!