Your understanding of these laws is flawed. A candidate volunteering information doesn't make the company liable for discrimination against them.
It's a common misconception that if topics like having kids or being married comes up in an interview then the company is liable to be sued for discrimination. It should be obvious that a candidate can't entrap a company by injecting this information into the interview when it wasn't asked. Even if the interviewers do ask, a discrimination lawsuit has a much higher bar than the topic simply coming up in the interview. It has to be demonstrated that the information was used to discriminate against the applicant, not just that it was discussed.
Your interpretation of my question is also flawed. I'm not asking "Tell me what you do in your free time." I'm asking them if they have anything outside of work that they'd like to share that would help their case.
> I suggest you talk to your HR department.
Please read my entire comment. The legal team reviewed our interview process and had no problems with it.
I think maybe your HR department has tried extra hard to scare you away from subjects they want to avoid, which has led to a misunderstanding of how the law actually works. It's common for HR professionals to tell interviewers that there are "illegal questions" or that if a topic comes up at all then you're going to get sued for discrimination. In reality, the legal bar for these cases is much higher. HR professionals just want to scare interviewers away entirely and drive the point home.
Asking candidates if they have an additional experience to share isn't an invitation for discrimination lawsuits. I suggest you open your mind a little bit and consider that some candidates may have more to offer than appears on the bullet points under each job on their resume.