Fay,
    When I was a boy, we were catholic, but my best friend was a mormon. The older children had their classes on Sunday, but the younger ones on Saturday. So instead of going back home while he went to class, I used to go with him (not sure if my parents knew). Then years later, when working in a refinery in the old Soviet Union, my coworker was an
ex-mormon, who had been a mormon missionary in Dublin. 
    Anyway, I think that both friends believed in the doctrine of preexistence of souls, which is a mormon doctrine. I don't know of others who teach that, there may be, but I don't know about it.