You could look up past threads, and get from them a few impressions.....
A. Good round-offs are about as easy to teach as double backs.....
B. Everybody has their own ideas about how to teach them and what to emphasize.....
My short answer is to teach them to start their cartwheels and round-offs by first losing their balance, and actually "falling" into the skill. This helps them build up some energy that can be used to create enough "impact" with the floor, which in turn creates the push-off during the snap-down that helps them stand up.
Another thought is to coach them to maintaing the strongest body positions possible while moving onto and off of their hands. The straighter their line are through their shoulders and core, the better.
Teach them to create the turn for cartwheels and round-offs by kicking the back leg with as much force/speed as possible, and that the skill starts like a front handspring until the back kick leg pulls their hips into the turn. Considering that last thought, doesn't it seem that most kids think the turn for a round-off starts at the top of their body (hands and arms), but IMO there is no energy in the arms since they're not anchored to the floor in the same context that the feet are.
My feeling is that the feet support the skill until the placement of the first hand, and since the turn needs to be well intiated prior to the first hand's contact, it's up to the feet and legs to create the turn. That leaves the body free to create a strong body line for the push-off.
Oh well! Like I said earlier.......We all have our own opinions and methods, some work

, some don't

, and some just confuse everyone but the person they originate from.....
