Threads are created by any user. Creating an entire forum is only for the site owner. I don't for see this as being created though. This is the first request I can recall on the subject, so the demand is nearly non-existent. Your best idea is to create a private group, though many times people join them but don't participate in them much. This is the idea suggested to most seeking forums for niche groups.
If you make a group perhaps broaden it a bit to something that is for family's with military members in general, rather than just parents of military.