Using the term 'Mormon' to refer to the the entire family tree including splinter sects is just a recipe for confusion. Adherents to splinter sects, excluding RLDS, number in the tens of thousands compared to millions of CoJCoLDS. The problems with CoJCoLDS are damning on their own without needing to conflate facts with fringe groups.
You should research polygamy in the mainline (Brighamite) sect if you haven't already. One of the last marriages to the the mormon prophet Lorenzo Snow was to a 15 year old. Snow was 57 at the time. This was not normal despite any assertion about children working.
Source: www.reddit.com/r/exmormon/comments/1c2omo0/the_wives_of_lorenzo_snow/