My new seedlings/plants are wimping out! under the grolights

These baby cuke, watermelon, and green bean plants are about 4 weeks old since being put in as seeds. The tallest bean plant just decided to drop its lowest 2/3 of its leaves 2 days ago and now others are wimping out today. They are not in the same dirt so a fungus or something couldn't be spreading between them. Not any mold growing on the dirt. No change in watering. Only the slightest change is that I fertilized them with very dilute Miracle Gro about 4 days ago. Is this enough to have caused this? I would like to keep these growing inside under grow lights for a couple of more weeks before putting them outside and "hardening them" to the hot texas sun. I'm hoping to delay putting them outside until Sept 1. Husband says that they might be needing the full spectrum of light outdoors.

They could also be too big for the containers you have them in and be root bound.

stephanietx, you were right.
I gave them one more day and they continued to look worse.
I took them outside to transplant them and the dirt was dry and there were too many roots for the size of the containers. I should have transplanted them a week ago. I hope that they survive. I have them under a little sprinkler timer setup to be watered twice a day. This is what is keeping my container plants going. Everything is looking better since I set up 2 sprinklers to water plants twice a day, about 3 weeks ago. Herbs are looking the best. Peppers are giving lots, but the jalapeno and anaheim are shorter, probably cause of the 100+ heat.

Do you have them under some kind of shade cloth or are you watering early, early morning and late evening to avoid burning?

I am using 5 container citrus plants (between 5 and 8 ft tall) and some hanging Wave Petunias to provide shade for the plants underneath! Its a crowded bunch in the middle of the patio but its working. I just moved some of the patio furniture this wknd, so I will arrange the plants in a prettier arrangement off to the side of the patio tomorrow.The bamboo teepee trellised cukes and green beans will go in the back, container citrus next, peppers in pots third row, herbs in front. ...... I used this sprinkler setup to set out starter tomato, cucumber and green bean plants. I had these all under growlights this past month, after starting them from seeds. They had that wimping out problem last week, but now look perked up these last few days under this setup. The tomatos are now between 2 and 3 feet tall and doing fine in their raised groboxes at the side of the house, getting watered 6 am and 6pm. 15 minutes of a fine spray, aimed low.
I am amazed that the herbs are looking great, in the middle of a hot patio! But, they are really in dappled shade from the taller plants around them, getting plenty of water. I have chives, oregano, rosemary and basil. I have some pretty 7 inch tall lettuce-leaf basil under grow lights now almost ready to go outside.