Other ways to get your point across.

What message is this sending? "It is NOT okay to fail in whatever you are trying to do". Reward the effort and let the results take care of themselves. Must allow failure over and over until results turn positive. I would compare this display of inmaturity to that of screaming at a player for not being perfect.
The child already feels bad enough having not been able to do what most of the others could do. Now you humiliate them.

What credentials did these trainers-coaches have? As David points out, you do not train a 10 year old the same as a 15 year old.

Possibility for injury does exist dependant on many factors using "Butts Up". Ridiculous waste of time. Shows the mentality of the coach/trainer/ and anyone else dependant on anything like this to get their point across.