Most of the kids joining VJTTA will use a two-handed backhand groundstroke.  They just don't have the muscle strength yet to hit with one hand on the left side of their body.   This article gives the basics of the two-handed stroke and highlights some of the features you need to emphasize when teaching it.

The starting position for the two-handed backhand is the same as that for the forehand stroke (this article is written from a right handed player's perspective).  The player is in a ready position, knees bent, feet spread at shoulder width, racquet in a forehand grip and cradled gently with just a few of the fingers of the left hand.

Once it has been determined that the ball is coming to the left side of the body, the player makes a unit turn by pivoting the feet, stepping toward the left with the left foot and turning the shoulders slightly toward the left.  At the same time, the left hand has gripped the racquet handle above the right hand.  

Turning the shoulders will bring the racquet parallel to the net.  This is the "show the logo" position, and is a key position in preparing for the stroke.  The hands and racquet have not moved from in front of the body. They are perfectly still, with the butt of the racquet pointing toward the player's stomach as both hands assume their proper position on the racquet handle.

I suggest the kids shift the grip of their right hand as they make the unit turn, from the Eastern Forehand Grip to a Continental Grip.  If they simply loosen their grip slightly with their right hand once their left hand has gripped the handle with an eastern forehand grip, the palm of right hand will turn toward the top of the handle and be in the proper position.

Holding this "show the logo" position, the player will move toward the ball, all the time watching the trajectory of the oncoming ball, trying to determine its pace, spin, elevation, likely bounce point, and probable location in the hitting zone.   Once these calculations are made, the player will stop moving with his feet and will begin the backswing.

Most players on the backswing should take their racquet directly back and down from the "show the logo" position.  Both hands should go back until they are near the left hip, or lower.  The butt of the racquet should now be perpendicular to the net.  The shoulders, too, should be perpendicular to the net.  The player's front shoulder is tucked under her chin, and most of her weight will be on the back foot.

The racquet has moved 180 degrees: the tip of the racquet was perpendicular to the net in the ready position, the face was parallel to the net while in the "show the logo" position, and finally the butt of the racquet is perpendicular to the net at the end of the backswing.

Some players might want to make a small loop on the backswing on the two-hander.  This is okay as long as they don't get their hands much higher than where they were in the "show the logo" position.  It is the racquet taking the small loop, not their hands and arms.  The end point of this loop backswing should be the same as for the straight back and down backswing described above.   The loop gives the player a little more rhythm and makes the swing smoother, but it is not necessary for beginners.

As the racquet nears the end of its backswing the player steps toward the oncoming ball and shifts the weight forward onto the right foot.  The racquet and arms are still moving backward. This will stretch the upper torso and provide additional power when the muscles contract and the forward swing begins.