Might be child abuse, stemming from ‘marrying’ child brides.
According to this wikipedia entry, he is wanted for child labor, as his children harvest nuts on his pecan ranch. (I though there was an exemption
https://en.wikipedia.org/wiki/Lyle_Jeffs
I though there was an exemption for child labor in agriculture.
Parental Exemption from the Agricultural Provisions of the FLSA
A child of any age may be employed by his or her parent or person standing in place of the parent at any time in any occupation on a farm owned or operated by that parent or person standing in place of that parent.
see p. 3 of:
https://www.dol.gov/whd/regs/compliance/childlabor102.pdf
BUT … are these children his children (because the law doesn’t recognize polygamy)?
So, not that I have thoroughly researched the matter, the issue is plain and simple polygamy. Not child or spousal abuse, or welfare abuse, or child labor per se.