I do have kids and I do think that's a job that should require a drug test.
A school bus driver MUST possess a Commercial Drives License with the proper endorsement, and according to the Federal Motor Carrier Safety Regulations, they must get an annual drug test, and a random drug test may be taken at, I think, every 3 months. Also a drug test can be taken at any time at the behest of the employer, if involved in a traffic accident, or a law enforcement officer deems necessary. (I possess a class "A" CDL)
I agree that a person seeking government assistance should be subject to a drug test, and if approved, subject to annual, plus random, alcohol and/or drug testing. I don't want my taxes going toward supporting their addiction, or repeated stints in rehab. If they are users, they must be clean/sober for 12 consecutive months before they are eligible to receive government assistance.
As for straight up health care, people should be drug tested, and if found to be a user, charged as if they have a preexisting condition and put in the high risk category. Alcohol users should be tested initially, and if a doctor deems them to be an abuser, be subject to the same costs as a drug user.