I started teaching my kids when they were 8-9 years old. They've handled, cleaned and fired almost every weapon I own. The only ones they haven't fired are my large bore hunting rifles, 30-06, .308, 7mm. My daughter was 9 the first time she fired my AR-15. My son was 10 when he asked if he could try my 12 gauge.
I've raised my kids around guns, I've NEVER told them they couldn't hold them, or look at them, as long as I am there with them. They know that they are NOT to touch them if I'm not there.
There is NOTHING wrong with teaching a child about guns. In fact it's the most responsible thing you can do if you own guns and have kids. Teach them young, and teach them right and then you wont have to worry about accidents, they wont be curious about them and go sneaking into you guns when your not looking.