No problem, saywhatkid. It's good to be clarify what I meant. I worked in this area and others may not be very familiar with it.
I agree that identifying drug addicted parents to protect children is a important societal goal. I just don't think that random drug test of welfare recipients is the way to accomplish that goal. There is nothing about being on welfare that would make a person more likely to have a drug problem than the general population. It's a sad fact that parents identified as drug addicts who do not recover have their parental rights terminated by the state, and those children are cared for and supported by the state foster care system (not federal welfare programs). There are not enough foster families and the states lose good foster families when they adopt the child/children in their care (often a foster family will adopt a group of siblings).
The way drug addicted parents are identified is by reports to child protective services (by a teacher, neighbor, judge or other adult who comes in to contacts with the neglected or abuses children). My state has a mandatory reporting law for children. Any adult who has reason to know of or suspect child abuse or neglect has a duty to report it to the appropriate authorities. Teachers, attorneys and doctors have higher duties (like reporting immediately within a specified time period). When an adult is being neglected or abused, an adult may report this information to the authorities (like family violence between adults). The laws vary among states.