The Division of Youth and Family Services, abbreviated to DYFS is the New Jersey state department which is empowered to investigate and address allegations of child abuse, equivalent to the Administration for Children's Services in New York State.
DYFS had investigated Marilyn Nesbit for abuse against her eldest son Daniel. She left New Jersey before action could be taken against her; while Daniel had been placed in a good home and was now living a fruitful life, she told her son Adam that Daniel had been murdered in its care.
When investigating the death of her youngest son Jacob, Manhattan SVU Detectives did not know of that investigation, because Marilyn Nesbit used her maiden name at the time, only discovering the connection after Nesbit, testifying before a grand jury, mentioned DYFS, not ACS, in a paranoid rant about how government agencies "destroy families". (SVU: Home)