At Children's of Alabama, all volunteers get a one step TB test and renewal annually, at our expense. We also do drug screens and background checks on all volunteers 18 and over.
We have a policy of drug testing of "at will" or "for cause" that would cover the teens.
Background checks on teens won't show anything since it would usually be a juvenile offense and the record sealed by the court. We do ask the usual question on the application about crime, etc that all employees are asked.