There seems to be a certain amount of misinformation around at present.
As I read it, the FMR 2 course is not yet a CiRF course. That change is yet to come. At that point the 12+ limitation will come in. (I actually think this will be a serious problem for most of our junior coaches taking that award, and needs to be addressed.)
According to the UKA document
here as UKA Level 2 Group Event Coaches (which is on my Licence) we are insured, and there is no indication of age limits. This is also reiterated on the FRA website
here.
So, it looks as if we FMR L2 coaches can coach any age group and be insured.
As for bashing UKA, without their support there would not be any FMR courses. When I became Junior Coordinator in 2008, one of my first priorities was to get a proper coaching course. UKAthletics funded its development and subsidised the pilot course. Because of that, 40+ people are qualified to coach Fellrunning to anyone. If you look around the junior clubs, I doubt they would be so well coached without this and they almost certainly wouldn't be properly insured.