Covering just Ubuntu, the Ubuntu UK Podcast is suitable for any age. It's hosted by a group of co-hosts and the content is generally well informed.
The Linux Outlaws podcast is very entertaining, covers a whole heap of open source software topics, but is not always suitable for children. The hosts Dan and Fab communicate their enthusiasm for Linux in a distinctive and amusing way, keeping the audience up to date on the latest software releases and Open Source news. They have an excellent theme tune which I think Dan wrote and played. If something is not really up to scratch there's no beating around the bush Fab's going to call it Crap! Their regular Microwatch feature is always fun too.