Make sure all of the computers are using the same version. There is no notification of new versions, and no autoupdater for the LAN activity, so if your main computer gets an update it might have problems thereafter, when flying against the others on the LAN.
On the other hand, with LAN-only play, you don't need to update the software at all... You can use old versions (even AH1) if its a better fit for your hardware. If your kids are using old computers, they'll probably find an all AH1 setup to be better.
Regards,
-Peabody-