It's hard to generalize because not all science fairs are the same. Some are ultra casual with the kids in sweats and judges in jeans, while, in others, kids dress up in their best clothes, even to the point of wearing shirts and ties.
Since you see this as a potential networking venue, I'd look for an adaptive outfit which would let you adjust on the spot. Jackets are great for this because you get a totally different look just by removing them or scrunching the sleeves. Sans jacket, a soft shirt with rolled sleeves, a good pant, and nice shoes looks professional, but casual, when talking to the kids. On the other hand, wearing the jacket when you are introduced at the start, and when you present the awards at the end, gives you a polished, professional look in front of an audience.
Personally, I'd avoid jeans, very trendy footwear, and anything cutesy or decidely casual. Science fairs are important to the kids and their parents because a lot of hard work goes into those projects and the judging is a serious business to them. Looking polished and professional is my way of honoring their efforts and keeping the focus on the kids, not me.