Thanks for posting this question, JenK! In my case, it wasn't my parents or anybody else. I'm a sort of a self-motivated outdoorsman.
I was born in a small mining town in Chile. Not much to do over there, so I spent as much time as I could playing outdoors and running away to our "backyard", the Atacama Desert, climbing hills, following old miners trails, and swimming in the one small creek we had some 20 miles away, until I joined the Scouts when I was 11 years old. Eventually I'd backpack most of the country and climb several of its highest mountains in college.
The interesting thing is that I got my younger siblings and parents into hiking and camping, and they love it now. Every time I take my parents camping I tell them that it's my "revenge" for them not taking me camping when I was little 🙂