If you watch the video GymCoachR2 refers to, you'll see the gymnast doing some things that don't get emphasized enough. I didn't stick around for the entire video, but whoever presented in the video is coaching, very well I'm sure, with a drill that need not be done considering the quality of positions the gymnast uses to move through the skill. Here's some highlights.......
She starts on one foot and begins her movement by falling slightly off balance along a straight forward line. This is great because it extablishes some energy in the correct direction.
Her back foot/leg is sharing the work by acting like a lever that tips her body towards the inverted position as she she moves her weight toward the floor. The back leg's contribution also allows her to concentrate/remain in a powerful body line from her hips to her hands as she places her first hand (notice please, her head is neutral). The back leg's effort as a lever also generates all the turn energy neccesary through the entire round-off, which is another factor in maintaining alignment and posture.
The gymnast arrives onto the second hand in ideal posture and alignment, and needs only a firm block through that side from her hand all the way through to her feet to create the mechanics for what many people call a "snap down."
Yeah. I call it a snap down when talking to other people I don't coach with, but it really is a "block up" that acts as a lever to tip the lower body toward the floor as the upper body rises into an upright position. My suggestion is to work your kids on cartwheels with excellent posture that begin as a fall forward, turn sideways as a result of a quickly lifting back leg, and makes the last 1/4 turn as a result of the block from the second hand.
The roundoff shown in the video is done on the tumb track, but could just as easily be done (cartwheels as well) on the spring floor by starting out (in that same position) falling forward from a fold up mat set up to provide a 3-6 inch drop. Make that a priority to teach your kids, preach good posture while inverted, and let the snap down take care of itself for the next six tumbling sessions. You can eventually progress to a r-o bhs, then a r-o 2bhs, then a r-o 2bhs bt.... all from a standing start from a stacked mat.
A good way to keep the kids busy is to set up a series of stack mats in a "round trip" configuration
Just one more minor detail...... This drill is going to create a roundoff that will do more than move them into the prime bhs position, but will dramatically increase their speed on a running start r-o bhs..... to the point of


. So you need to be careful, and tell them no r-o bhs with out your blessing, and then only out of a gentle run for the first one or two. Really.