I teach my first-year law students every year that you're only allowed to conduct a physical or mental examination of a party. That's true in federal court. That's true in California state court. It's true pretty much everywhere they might practice.
I try to make the rule memorable by recognizing that it's a principle that's not without cost. Say you have an eyewitness, and the critical question is whether this eyewitness has good vision or not. The easiest way to figure this out would be to order an exam. You could do that if he was a party, rather than a mere witness. But if he's a witness, no matter how critical the inquiry, no matter how critical the exam, a court can't order one.
We fear that compelled physical or mental exams of mere witnesses are too burdensome, plus there are enforcement and liberty concerns (will we really strap them down if they resist?!) that don't apply to a compelled examination of a party. Seems crazy, in a way, since sometimes a lengthy deposition is far more burdensome than a 15-minute visit to the eye doctor. That's the rule. Know it.
The California Court of Appeal reaffirms that rule here.
The trial court thought it could not only order a mental examination of the minor plaintiff (which it surely could), but could also the parents to submit to interviews with the defense forensic psychiatrist.
Nope. That latter thing you can't do. They're not parties. No physical or mental exams. Period.
The trial court got it wrong. Hopefully my students will get it right on their exams.
And now, you'll get it right every single time.
Only parties. That's the rule.