Where do you study, which leads to questions of how much or if the dorms are conducive to study, and can go a few other directions from there, like what’s the library used for these days, or where do most people study?
How was major selection for you: hard to get into a program, how did you choose, etc.
How hard to find a job, do you have one other than this, how many kids work, on or off campus jobs, etc.
What did you do last (or next) weekend? Not to be creepy, but to illustrate what a random weekend looks like. Also how often do most kids go home, or have friends visit them here.
What sports or arts events draw out the kids? What is school spirit built upon? Are there annual things that are unique to this school? You might be able to answer this on the website or Niche or whatever, but true energy can come through to really illuminate some answers.
Parents can ask questions and participate, but only when the kids are not carrying the ball. Leave space for them to jump in, but don’t sit on a decent question during a dead spot just because you asked the last one. Most people are happy to have someone else ask a question they are interested in hearing the answer to. My DD was chatting with a quieter student she met on one of our tours, and when that girl asked her a question DD just said “Well hang on, I’ll ask.” Not shy, that one.