How do you prevent the kids(middle school) from accidental throttle up with hands near the prop. I have had a couple near misses myself.
First, we set up a throttle kill switch. This is a good idea for anyone from Middle Schooler's to the most experienced pilots.
Second, a simple rule: When indoors you can have a propeller on your motor OR a battery plugged in, never both. The only exception is when you are testing current draw during a static run-up in which case someone is holding the airplane. When at the field the throttle is to be cut until you are ready to launch.