All mine are outdoorsy ... been out walking with the dogs since they were all really small (and actually, I did push them across muddy fields in a pram when they couldn't walk far ). They walk for miles, climb trees etc.   
  
Exposing them to anything they're interested in and letting them explore how far they want to take it the way to go. If they're committed to a certain number of lessons in something or a course or whatever, they have to finish it - not quit half way through. If, at the end, they don't fancy it that's fine but once committed I do make them follow through. The girls did gy