To stick my oar in- I live in Seacombe and my daughter did the Rainbow / Brownie thing. At 17 years old, I can't visualise her joining a group involving 10-13 year olds (kids).
For what its worth, i think you have a valid idea but its a matter of 'catching them young' and then maintaining the interest..
Apologies if you find this patronising.,
Ohhhhhhhhhhhhh! Jer-e-my Cor-byn