The only "child" it could be talking about is one of the compilers, if a port you were upgrading was using the compiler_blacklist_versions portgroup, and MacPorts was trying to determine what version of the compiler you have installed.
This suggests one of your compilers is not working properly. Reinstalling the command line tools might fix that. If you're not already using the latest version of Xcode, you could upgrade to Xcode 4.6.3 and then upgrade its command line tools in Xcode's Preferences window, in the Downloads section. If Xcode claims the command line tools are already up to date, you could reinstall them using the installer available at http://connect.apple.com . If that doesn't help, please try again with the debug switch ("sudo port -d upgrade outdated") so that we can see what compiler it was trying to run at the time of the crash.
