Hope this isn't too late for your travels - I joined recently and was playing with the archives...

I guess you will be somewhere else and just stopping in Frankfurt to catch a plane? And you already have a rental car before Frankfurt and you will want to drop it off at the airport? Hey, I'm supposed to be answering questions not asking!

The reason for asking is that it might affect your options. If you are mobile and want to and want to do something around Frankfurt but not in it, there is two options for the younger folks:

One is Hessen Park: http://www.hessenpark.de/frame_finden.html which is on open-air museum of life in the good old 1800s. Old methods to brew beer (maybe a 12yo isn't so interested in that), baking bread in a wood fired oven (for sampling!) and such in a setting of many buildings from the past couple of centuries. I think you can see the variety of things from the website (all in German).

Another option is the more fun-and-games place called Lochm�hle: http://www.lochmuehle.de/ You can also get a feel for what they offer from the website.

A little further out (but not bad with a car) is Wunderland http://www.taunuswunderland.de/standartneu/start.shtml

If you are staying in Frankfurt there is the the ZOO with the dark room. The nocturnal animals are active and your are in the dark! http://www.zoo-frankfurt.de/

And there is the chance to see Frankfurt from above with a trip to the top one of the skyscrapers (and the website is in english) http://www.maintower.helaba.de/e_home.cfm

But what about the hotels? The closer you get the more expensive they are. I know there is a cluster of more reasonable hotels around the towns/suburbs of Morfelden and Walldorf. These areas are not in Frankfurt - you would need to drive or take a train (which is often easier!) But I can't give specifics on these hotels because I never really been there. Have you tried the searches through google like: Frankfurt airport hotel close or expedia or such?

Maybe some of that helps? Post if I can be of help...

Regards, Brian