you may not like it, but.......
Most children, regardless of how mature they look or act, have not learned through practice yet how things are in the world. There are always exceptions to the rule, but that is one reason most vehicular accidents happen to young age groups along with a host of petty crimes that normally don't happen to people in the 20's and up.
Also in most states, the adult guardian is liable for crimes and situations that the guardian knowingly alllows the minor to do.
Lastly...in a lot of states an unsecured firearm left in the presence of a minor is , of itself a felony.
So, my opinion is that a minor has no business with a firearms unless he/she is being supervised by an adult guardian in some type of legal shooting activity.
If a child is alone in an area that is risky or if the home is not safe, the child should not be left to his own devices and doing so is in fact illegal in many states.
Having children is a reward most of the time....but make no mistake, it involves many sacrifices for the parent/guardian.