With the diagnosis of "flu", would any of the doctors have prescribed antibiotics. Sometimes, we INSIST that our kids be prescribed antibiotics. It's called "playing it safe" and using your "gut" feeling.
Flu is not treated by antibiotics, but sometimes they are administered anyway because of the emotions of the patient. (No antibiotics? Don't you love me, doc?) They're as good as a sugar pill for effecting cure, but sugar pills have been known to work.
If this is a flu, and it isn't menangitis...if the kids were healthy otherwise (not asthmatics, or chronically ill)... there is cause for concern.