I learned how to fish with a cane pole. Then again, my daughter learned to cast when she was four. I'd have to say that any light action rod and spin cast reel would be best. The closed face reels are easier to operate but the open face is easier to get the snags out and they're not so difficult that a child can't learn to release.
Take the kid into the back yard and lay out a hula hoop or anything else that approximates this shape for a target. Have them toss a lead weight into the circle. This will teach them touch. When they get pretty good at it, take them fishing.