In collaboration with the schools in our area, my company (a major employer in our community) is holding this during summer vacation this year.
We organize kid-friendly activities that relate to the work we do, and restrict the age range from 9-14 so we can plan activities that are age appropriate. We get a lot of positive press and the kids enjoy it tremendously. Nobody just sits and watches Mom & Dad all day long. This is good because my kids wouldn't be allowed in my lab- restricted to adults with safety training (i.e. small amounts of radiolabel, small amounts of hazardous chemicals, perfectly safe IF you know what you're doing). Instead, they can do such things as go to a conference room for an hour to learn about statistics from a statistician - calculating what percentage of their bag of M&Ms are brown, the average, median and mean number of brown M&Ms for everyone in the room, then go to the auditorium for a chemistry magic show, then go to the product testing area to "test" different types of candy, etc.
This is for both boys and girls.