Well I would say that is your problem. The plants pictured are most likely suffering from nutrient dificiency, most likely a lack of Nitrogen. Those plants are far too mature for you to not feed them any nutrients. If you were starving to death, you wouldn't look much better.
Worm castings are very low in Nitrogen and is really used as just a soil conditioner. It allows the soil to drain better, but does not fulfill the necessary nutritional requirements of the plant. I would feed them some fish emulsion that is high in Nitrogen. You should see an improvement in a matter of days.
Fish emulsion is the best fert. I have found for vegging plants. It's usually high in Nitrogen, which is mainly what the plant uses when in veg. growth, and is also rich in phosphorus and potassium as well. In addition, it can be mixed into a dillute mixture and fed to very young plants with virtually no risk of burning.
However, because these plants were starving to death, any fert. is a good fert.