You both may like the
Doctor Who podcasts from Darker Projects. They are in the vein of the "old-time-radio" stuff in that they are a serialized drama (i.e. actors for each part, sound f/x, etc.). They hardly ever put any new ones out anymore, but they have a pretty long backlog. Darker Projects puts out a
lot of that kind of stuff, but I don't know how much of it is good
or appropriate for an 11 y/o. I've been meaning to check out some of their other stuff, myself, but just haven't made the time for it, yet.
You may also enjoy
Fortress Draconis. It isn't finished yet, and has gotten really inconsistent in its releases, but it's been a pretty okay story, so far.
If I find a podcast I like in iTunes, then I usually check out the "Listeners also subscribed to:" sidebar. That's how I found EP.