I would keep on with the Scouts (if it were me) take on the mentoring tasks and when #1 son is finished THEN tell them all about how atheist you were the whole time.
I discouraged my kids from joining ANY pseudo-religious group. Thankfully they were far too individualistic for group activities anyway.
I discouraged my kids from joining ANY pseudo-religious group. Thankfully they were far too individualistic for group activities anyway.

"The Universe is run by the complex interweaving of three elements: energy, matter, and enlightened self-interest." G'Kar-B5