Would it matter either way if they knew he was a child? The key point here is the perceived presence of the gun, which makes a child just as dangerous as an adult. As to how easy it is to differentiate a real gun vs a toy gun, it’s not when one’s being pointed at you. If police respond to a call for someone with a gun, and that gun is being brandished or pointed at them, do you really expect them to be able to briefly see that gun i linked to and discern that the barrel diameter and weight mean its not real?