My rules are simple - no toy guns that look anything like real guns.
I was crossing a parking lot when a man appeared from behind a van holding an Uzi and yelling angrily at someone I could not see. His young boy then also walked into view. I think he had taken the very realistic toy away from him for some infraction. Our eyes met and he turned red realizing he had scared the hell out of me. We looked at each other for a moment and then he walked to the van, threw the toy in,and walked away.
That is part of why I do not allow my kids to play with toy guns. I live in the People's Republic of Maryland, and while many of our cops are good, at least a few of them are anti-gun morons. I never wanted to put the occasional stupid cop in that awkward position. I also never wanted my kids to think it was okay to point anything that looked like a gun at another person except in self-defense. I don't want any overlap between what they learn with a SuperSoaker and what they learn about real firearms.
All of my kids shoot fairly well, and it has probably been years since anyone in my family except my wife hit outside the black when at the range. They all treat shooting as an enjoyable activity to take seriously, which I love.