[Maru]

The FLDS practice this. Polygamist religion that married out all their child brides and was completely cut off from the outside world... well, the "unaware" folk were kept out of the loop... the Elders secretly benefited modern life and the numerous child welfare paychecks

I guess Mormonism is technically an American religion so maybe it's not talked about there? I think they're basically Christianity but with a modern prophet, but they used to practice polygamy in the States...