All my little ones were in full leaf and actively growing when the first frost came. As long as it is only in the upper 20's or low 30's just overnight and warms up the next day, I wouldn't be too concerned. It's nice to put them next to a brick wall or something else that will hold the heat overnight. Mine are all still outside, but in sheltered locations. Of course, its 60 degrees here today, but has been in the 20's already.
Scott