I have two pretty early memories.
1. I was on my first trip, so I was 5. We were only in Orlando because my mom was on a business trip, so me, my dad, my mom's coworkers kid (my age), and his dad went to MK for a day. I only remember two things, a) I was really disappointed that I didn't get to go to Sea World and b) When we got to the Sword in the Stone, my friend and I got really competitive trying to get the sword out. We thought we would actually be able to to it. Our dad's had to drag us away.
2. On either my second or my third trip, my dad and I stayed for MK EMH, so it was late. My dad finally got me to go on Splash Mountain for the first time. I was so scared for the drop and closed my eyes most of the time, thinking it was around every corner. When we finally made it back, the CM's told us since their was no line, we could stay on again if we wanted. I shrieked no, that I wanted to get off, but my dad convinced me in the end to go again. This happened 6 times, me begging to get off between every time. Of course, by the end I was really having a blast.