Just a couple of comments. First of all, BTCV have a franchise called Green Gym, which provides workouts by doing woodland and conservation work. They want a lot of money for running it, and you may fall foul of their patent if you try to do similar, which might rule out Tracy's idea.
Second, you need to state your qualifications in fitness training on your web site and also REPS registration. I guess you have full qualifications to at lest Level 3 in fitness training, outdoors fitness and children's fitness, but your web site doesn't show this. Without these, and appropriate insurance, them you will have difficulty getting a site willing to let you run classes. I know. I am level 3/4 qualified in fitness, outdoor fitness, Nordic walking, cardiac rehabilitation, personal training, exercise to music, GP referral and it isn't straightforward. I'm sure you've thought it through, but be good to see on your web site.