Here is the rule for ya. They are totally allowed to line up on the center. They can even hit the center after the snap.
3rd and 4th grade there just not allowed to hit the center until the ball reaches the Qb. No where does it say they cant line up over center. thats mighty mites rules where there not allowed to line up on the center.
Article 2:Section 19 Page29. Center Protected: In the 3rd and 4th grade level, the defense
will not be allowed to make contact with the center on a deep snap, including
shotgun offense, until such time that the ball makes contact with offensive
back or when the ball makes contact with the ground not direct hand to hand
contact.