I don't remember what anime I watched first but what I remember was watching these in kindergarten to 1rst grade
Pokemon, Digimon, Yu-gi-oh, Dragon balls,
along with the anime they would show on adult swim.
which I think at the time was Gundam, Big O, and Serial Experiments Lain. I didn't understand what the hell was going on but my young mind was fascinated by it to the point that I'd stay up every Saturday watching them.