Besides being able to legally make "dam" jokes in front of your kids, the dam is an amazing place. And since they have been working on the highway bypass it is magnificent. There is a great parking garage with easy access to the visitors center and take the dam tour and there are dam bathrooms (see? i'ts fun). It is a good tour for probably 5 and up. Going down inside the dam may be a little scary for younger kids and if you are closterphobic. My dad had to down 6 pack of Sokes to muster the courage (That's how mormon's muster courage).
Plan for almost a full day for the trip out there. It will be about a 30 min drive from the strip. Here is a link to the dam website for tour and money information. Yes it costs. But it is worth it.
www.usbr.gov/lc/hooverdam/
