JUNIOR OLYMPICS MIXED DOUBLES SERVING RULE
The girl may serve to either opponent. But the boy must serve to the boy -- such that the serve clearly appears to be intended for the boy to return and so that the served ball could bounce and be played on the boy’s side of the court.
If the side of the court the boy is defending is unclear (if he is standing at or near the center of the court), then the server may ask the receiver to declare which side he is defending.
After the score or “second serve” has been called and before he serves the ball, the boy should indicate which side he is serving to -- the one the boy is defending. After that indication, if the receiving team chooses to switch sides, the boy may serve to the left side of the court if he chooses without regard to which side the boy is on when the serve is made.
Any serve that fails meet the above criteria is a fault serve. Should the girl return the boy’s serve and the serve otherwise comply with this rule, then a “no serve” will be called and that serve will be repeated.