Step 1: Know your purpose
The most important lesson kids can learn about guns is that firearms can do a lot of damage and therefore need to be handled with caution. A fun day spent on the range with reactive targets can really hammer this lesson home. When I thought my kids were old enough to absorb the point, I loaded them up and took them to the range with me. Our targets that day included pumpkins, zucchini, half-rotten tomatoes, and a several jugs of water.
The safety issues are included in step 2 and 3 on the next page . . . including the difference between the NRA rules versus self defense family rules . . .