I work with lots of youths, and there a number of them that don't adhere to the proper push-up position. Rather than keeping their bodies straight, they will stick their butts up in the air. When they do "push-ups" they tend to just move their hips up and down while keeping their arms static.
Understandably, some children lack the strength to hold themselves up, but I want to encourage the strength build-up over time rather than have a bad habit develop. I get the impression that the youth who can't do a proper push-up will just go on auto-pilot without consciously telling their bodies what to execute in terms of movement and control.
What are ways to move towards the right position and maintain it (without the use of any extra props)? Saying "keep your body straight/flat" or "don't stick your butt up in the air" does not click for some younger ones. Are there better ways to describe what to do and "trick" their minds to get their bodies to listen?