I was never in any proper cadet force but I did flirt with a military career - I had work experience with the paras (I don't know if they offer this anymore!) and, a few years later, a residential stay at HMS Britannia with a bunch of officer cadet types. For better or worse, my hernia put paid to that line of work. Anyone who has gone through recruitment can attest to how ludicrous MOD medical checking is and I just butted my head against a brick wall.
At the time the para work experience was very, very hard and I'm still unsure how beneficial it was. I recall Corporal what's his chops carrying four cheapo halfords MTBs out of a shed for an 'adventure' bike ride and bellowing 'right which of you retards can't ride a bike?' and there was all kinds of daft arbitrary collective punishment. Knowing what I know now about bikes, I'm pretty sure no one was carrying any repair kits or whatever, and if anyone had caught a flat they'd be in for a 30 km trundle home on the rim. I was also witness to a lot of toxic behaviour including racism, misogyny, and general bullying. On the other I was definitely pushed to new limits, I was not a sporty kid but I found there were things I could do, like doing (what at the time) was a long bike ride, long hikes, problem solving exercises and so on which I do think was bona fide quality character building.
If/when I care for children myself I think I would steer more towards adventure organisations like the Scouts but I'd find it hard to say 'no' if one of them asked to check the cadets out.