Don,
I have taken specific steps to ensure my son uses proper safe handling of his toy guns, even though they're "just toys" because he's still at a young age when understanding the difference between a "safe" NERF gun and a dangerous "REAL" gun is difficult.
He practices safe handling (he'll even unload a NERF gun before handing it to someone), and has been taught that he only shoots at targets. (Targets includes actually "targets" but also some of his action figures, toy cars, etc, but never people) When we do play shooting games with each other, he brings daddy all of the guns we'll use and daddy checks them out to make sure they're safe. Only after daddy says it's ok can we play shooting games.
We had guests who don't have guns over with their kids. When one of the kids pulled one of his NERF guns out of his toy bins, he told hem, "We only shoot at target" then came to me to ask if they could set up targets and shoot in his bedroom. We set up his Transformers and they spent the next 2 hours shooting at transformers in his bedroom. Our guests commented on the discipline he has.
When he's a little older, he'll start getting introduced to the real guns and as he develops the understanding of the difference, he'll be allowed to start playing shooting games with toy guns and people as targets. It's been my experience its easier to start with the general (we only ever shoot at targets / we always use safe handling) and then work in the exceptions when specific activities are allowed than to start with the exception and then try to correct for the general.
There's no risk in having a child treat a toy gun like a real one, there's a huge risk in having a child treat a real gun like a toy.