You don't use Illustrator for pixel art.  Illustrator is a vector program, it isn't meant to be pixel perfect, the program doesn't even use pixels to process things.  It's becoming blurry because the program is attempting to take those vector lines and convert them into anti-aliased pixels.  You might get better results if you can figure out how to turn anti aliasing off but I don't even know if that's possible.  It will probably be easier to just start over with a raster program like Gimp, Photoshop, Krita, Paint, or pretty much any other program that isn't just for painting or vectors.  I recommend that you choose something that supports layers and animation and that you know for a fact you can turn off the anti-aliasing for the tools.

If you want to stick with vector art you'll need to start with a much larger canvas, say 512 or 1024 px so the pixelation when exported out as 64 px isn't so bad. You still might need to do some clean up afterwards in a pixel editing software.

This is a vector art example done in Inkscape.

g5515-95dpi.png is 246x215 exported at ~96dpi.

g5515.png is 64x56 was exported at 25dpi.

Maybe if I scaled down with ImageMagick I could of received a better result but the pixelation doesn't look at the bad without any touch ups.