Mumps exposure

Welp we have a possible Mumps outbreak at a Army post close to where I live. Can this be caused because of unvaccinated children? Or could it be caused by maybe the constant traveling overseas that the soldiers and families do? The article states the children who have it attended the Elementary school on post so I guess that means now all the other children and staff may be at risk. It hasn’t been confirmed anyone else had it tho, just that one family.