Noone can say for sure from just these pictures. The bothersome part of the second picture is that the newer leaves should be getting bigger and with longer stems, but appear not to be. And when no problem is visible above ground, the answer may well lie below ground. In my experience, failed squash starts in the garden are the result of Symphylan attacks on the roots underground. That may not be an issue in your area, but something else may be messing with the roots. A root inspection may yield some clues at the expense of destroying a plant. The other thing that comes to mind is too much nitrogen.

Thanks much for your input! I do see what you mean about the new leaves being smaller than they should. Before planting I amended the soil with pumpkin power 9-3-4 & something for pumpkins biogrow endo. I also treated soil with Actinovate an org fungicide. I haven't done much since except feed with seaweed. I know too much nitrogen can cause yellowing of leaves, but wouldn't stunted growth indicate a lack of nitrogen? I really appreciate any advice - feeling so deflated that my plants are so young and looking so sickly!!