You'd be surprised how many times a non-smoking order is put in place as part of a protective services case. If it is a case that is in court, these case plans are weighed heavily by the judges hearing the cases. It depends, to some extent, on the worker. Personally, the only time I would include such a condition in a case plan would be in the situation where the child already had a diagnosed health problem that was significantly aggravated by cigarette smoke, such as asthma, AND where the parent was not one who had much awareness or who didn't make much effort to protect the child himself. Then I might include that the parent was not to smoke in the same room as the child. There are workers, though, who because of their own personal anti-smoking biases, who will demand that parent NEVER smoke around their kids and if they discover that they do, might make a big issue of it as failure to comply with the case plan. Then it can make a big difference in court.
Pretty soon they will be legislating what you can eat and/or feed your kids on your own time.