Taking in children that were orphaned simply is not slavery and certainly not the same system we are referring to racial chattel slavery in the US.I did both are a matter of record
Act_in_Relation_to_Service made African American slavery legal in Utah
act for the relief of Indian slaves and prisoners made indian slavery legal for a period of 20 years after capture, which increased it from 10 which it was under the old Mexican law.
Both can be found online and at wiki, I provided the actual act for relation to service in other post
As to not taking captive children as somehow not being slavery...….would think thats rather subjective as the children didn't have a choice of where to go or remain with their parents...….who had done nothing to deserve death. Little different then attacking Indian villages to make slaves of the women and children
this has Indian one text https://collections.lib.utah.edu/details?id=716787
They had their own territory to do what they wanted to do...…..and what they did was include slavery both for Africans and Indians.
I've also already references quotes from Brigham Young himself speaking against Southern secession and proclaiming it's slavery it's doom.