Coachkyle is right in that there is no rule stating where the pitcher has to be. Technically, you are REPLACING the pitcher, therefore you now have an extra player on the field.

What I want to point out is that the mite player should be positioned such that he/she can see the batter and that the Adult does not move on a hit ball such that the view on the player is blocked. SAFETY of the mite player is the number one objective here, since an astute coach should be able to pitch to the 'sweet' spot for the batter which can constitute into harder hits.

When we were in 1st year mites, one of our players was positioned slightly behind an adult pitcher. Ball was hit right at the player; ball hit her on side of head - player went to hospital (had slight fracture to skull) and was out of ball the rest of the season. From then on, we ALWAYS positioned our pitchers on the baseline (2nd-3rd); if the batter bunted that was okay because the max run limit prevents runaways and we could always get those runs back.

Remember SAFETY of your players comes first - and adult on the playing field is a hinderance to players seeing the field of play.