Are you judging? If so, there will be a rubric to judge to, and sample questions. You should get some training materials before the event, possibly a training session the night before the tournament, or at least a session with the head judge on the morning of the competition.
Ask them what the coolest thing is about their robot. Ask them what their favorite mission is. Ask them what they learned about teamwork. Ask them if they like programming or building better. Ask them if they are nervous about their presentation and did they learn anything interesting while researching. Also, ask them if they had fun this year, did they make new friends and teach them all the good dances. I was really proud of my kids for getting out on the dance floor every competition. Have fun, remember most of them are middle schoolers and really goofy. Let them know goofy is the new cool
Get some guidance from the organizers on when the best time to mingle actually is. I like Wendy’s questions! Remember these teams have 3 tightly scheduled judging times (where they may be asked similar questions) besides all the robot rounds. I’m still recovering from the fun at our 74 team state tournament a week ago.