the #1 reason that kids have a problem with just the squat on is that they are afraid they will miss one or both of their feet and then 'pitch' head first off the bar to the floor. this is a different problem than jumping to the high bar. when you couple both fears, the task is too daunting and they fail on the first...the squat on.
i have posted a drill for this before. best thing to do, and something they can work on by themselves and unsupervised, is set up a fat mat or stack of mats under the low bar so that the mat/s come to the bottom of their feet when they are in straight arm support.
you then instruct them to 'pull their pants down to their ankles'. they must keep their 'pants'/legs against the rail.
when they get their feet up to the bar, they then lift their knees and flex their feet and 'press' their feet on to the bar. if they make it, they do. if they don't, they don't. this is done without swing. it's called 'static'.
you kill 2 birds with one stone with this drill. #1, you condition the core and quad muscles. these muscles are important for everything. but specifically, your core and quads are what control pressing to handstand on floor, or beam, etc; but also gives them the strength in reserve they might need in the future if they miscue a cast handstand on bars, either from static or casting, and will have the ability to 'press' it out so they don't suffer a precarious fall.
#2, you are training the movement pattern required for casting to a squat on no matter how high or elevated that cast may be.
#3, the 3rd bird in this whole thing is the elbows. you can't perform this drill correctly without keeping your elbows squarely over the top of the rail. when kids cast to anything, more often than not, their elbows will be behind the rail and the cast and they can't get up to a handstand or over the top of the rail to put their feet on or their shoulders are to far forward the rail and they fall forward and drop on their thighs on the rail. and that hurts! additionally, if their shoulders are to far forward they can't get their feet on either. so then, if they can do the drill to completion, this means that they were able to keep their elbows squarely over the top of the rail on center. moreover, they are working all of the upper body muscles required to stabilize the upper body when working above the rail. this stupid little drill will lead to better and more effective cast handstands without incident. not just a really good cast squat on.
finally, they are practicing on a station that will not create a precarious fall and possible injury. very non-intimidating and non-threatening. and if they still are afraid, then you raise the mat again so that it comes up to their knees so that their knees will be bent in support. then follow the above steps.
if you have additional questions not explained concisely, please ask.
