The preterists say the following about Matthew 24:34:
One of the meanings of the Greek word translated "generation" is "family":
"genea, a/j, Ion. geneh,, h/j( h`, Ep. dat. geneh/fi: (gi,gnomai): I. of the persons in a family, 1. race, stock, family, Hom., etc.; Pria,mou g. Il.; evk geneh/j...