If the leaves were not tattered and fallen off, they would be fine. If they are tattered or dropped off, they become susceptible to the various environmental stresses.
Good luck with your saplings.

I've seen young tree's leaves turn yellowish after weed killer is applied to the lawn, this is not whats happening with yours, right?

Take some samples to your local extension office and they will most likely be able to tell you what's going on. There are several critters that feed on oak leaves. Their damage is not really harmful to mature oaks but can be very stressful to saplings.

we have had serious drought this year. it could be that?