No Worries, Everything's Fine at the familyfriendly "Bullets and Burgers Gun Range" .... It was just a Accident ;-)
With a 12 Years Military-Experience, I would still be fucking pissed to get shut in the Head, by a 9Year Old, under my Supervision.
Next Time around, you should instruct the 5to7 Years Old. They're only allowed to use Small Caliber, which may not penetrate your Scull.
No need to explain, how I think about, training Kindergarden on fucking Firearms.