Help me improve my pitching

First of all, whats the average speed of an around 8 year olds fastball?

I am 12, I can throw a fastball and I think a change up. I want to learn a curve and I wanna improve all my pitches, can someone tell me the best way I can improve my pitching?

Can someone tell me the easiest way to throw a curve?

Stick to a fastball and changeup. Work on location, and don’t throw a curve ball.

CanadianBall51 is right. You’re awfully young to start messing around with a curve ball or other such pitches—you need to wait a couple of years until certain growth processes have been completed. So continue to work on the fast ball and the changeup—but if you absolutely must add another pitch to your repertoire, there’s the palm ball, which puts no added strain on your arm because you throw it with the same motion as for the fast ball. And by the way, it makes an excellent changeup, so you would have two of them.
In the meantime, you can work on sharpening up your control, refining your mechanics, and throwing strikes. It’s never too early for that. 8)