I think it's our responsibility as parents who enjoy the outdoors to pass this type of stuff on and make sure it's a positive an experience as possible (sorry to hear about that incident on your second trip!). We need future generations to not only care about the environment in a vague sense but to have a personal connection to it.
I took my son for the first time when he was four. The next year, we went three times, in spring, summer, and fall. We didn't get an opportunity to go away the year after that but our property is nice and wooded so we camped in the backyard a couple of times. These last two years, he's been more involved with sports and other activities so we've taken a break from overnight or multi-night trips and just done hikes. Next year, I have two weekend trips planned for spring and summer. I'm planning on taking my now eight year old son on one and my four year old daughter on the other. If only I could get the missus interested and we could all go at once.