In our school district we'd have to name it "Taxes Hold 'em" since our tax dollars are used for the schools! Here is another idea that might be interesting...could you ask the local Home Depot to come with the latest tools and maybe hold a workshop on something...followed by another booth with a sporting goods rep there with some of the latest and greatest in sporting goods....
As far as a poker night, I would never promote any alcohol, because you are ultimately responsible...but you could have a poker night with chips made by the children (have them laminated and cut out) and then see if you can get a local restaraunt to donate a couple of dinners for two and that would be the prizes for the top 4 finishers.