On the xbmc blog they have details the changes in the June and July development cycles of XBMC 13. In the last couple of months there have been lots of changes including new CD ripping features where ripped CDs are now automatically added to the music library and you can now rip in AAC and WMA format.
In this build profiles can have their settings locked so if your kids have their own profiles you can lock the settings down and stop them messing with your carefully designed setup. There are also improvements to the caching over the network so if you experience lags over the network then this change could help.
The Android version gets Airplay support so it can be used as an Airplay receiver plus XBMC can also be used as the default player for the Android file browser. Other changes include Thumbnail generation has been improved so they should generate much faster and the Windows and OSX version also get copy and paste support.
Remember this is still an alpha version so there are likely to be bug in it, more details and the download links on the xbmc blog.