things you can check at that age
toenails & nail color (if you're raising shadeds & dilutes especially; all the nails should be the same color)
size (ones that are obviously larger than the littermates, with longer ears, are probably false dwarfs)
tail problems (wry tail, broken tail, etc)
tooth problems (although they can change with age, some have obvious problems at that age already; look for one where the top tooth is flat on the bottom, instead of pointed, like a chisel. that's the easiest way to tell on young ones that they might have simple malocclusion).
color DQs (like white spots. a few exceptions; such as light undercolor on dilutes or lack of shading on a shadded. that might go away. What color do you have? I could give you specifics then)