I stationed the door for a lot of it, handing a bag to each kid so he or she could keep stuff from or made at the tables. So I felt like I had to act super excited and enthusiastic, because lots of the kids would walk in with their parents, look around, and get the stunned scared deer-in-the-headlights look. Then I'd smile and say welcome and tell them to go have fun and suddenly they'd light up, like they were OFFICIAL now.
The goal is to make little engineers. Parents are required, but often turn out to be a necessary evil. Hate to say it but engineer dads are sometimes the worst, they'll just about push a kid aside to play with the gears rather than stand back and let the kid do it. But I know from experience that their kids are more likely to become engineers just based on geek genetics, so I don't sweat it too much. all things considered engineers in general make good parents.
Second worst are the checklist parent who wants their kid to spend an equal amount of time at every table. We set up chairs in the middle and a video, it's the "tired parents" area, but it's also great because a lot of kids find a table they love and stick with it when their family stops being so concerned that they hit everything. Some little girl practically built the Louvre Pyramid out of toothpicks and marshmallows today.
I did accidentally run into some guys from work and said Hi to them in my over-perky morning kid voice, then realize how weird that probably sounds... especially since I avoid talking to people in the office until 10 or so when the coffee is kicked in.