I have only ever taken museum tours in France, and only because those were particular places which you couldn't visit without a guide.
I did tours for children several years back, though not in museums, but through a forest. So I had a little experience there... and the first tour was indeed a kid's tour. Second was for adults. How did it go? Surprisingly well. My great advantage was that I was familiar both with the subject matter and the conception of the exhibition (though not every single exhibit), so not only was there a lot I could talk about, but I also actually knew what was important and what wasn't. I actually felt competent and comfortable in my role, and the people all seemed to be interested. I'm glad I can do something like this for a student job instead of filling up supermarket shelves or the like.