My seedlings looked a little bit like this and the continued rain in June after I planted them, didn't help either. I think it is hard to start cucurbit seedlings and then transplant them. But it can be done! They are a bit yellow as you mentioned and need to be feed. The seedlings' nutrients get washed out when there are in a little pot. I use Dr. Earth but you can use other fertilizers. I believe in the beginning they need more nitrogen and as they start fruiting they need others more and nitrogen less. I think it is more potassium for the flowering stage among something else. Nitrogen helps with the green leaves. HTH!

There usually isn't a need to start pumpkins indoors, that's probably why they are yellow and have brown edges. Just throw some seeds in the ground, I bet they will catch up to your transplants.

Yes, in tropical Florida there is no need for indoor propagation. Behind modern glass your plants get no UV-B rays. The lack of UV-B makes the hypocotyl too long.
But the rest of symptoms is Alternaria blight. You can grow such plants and they will survive with a perfect fertilizing management, but you will have more alternatia then in your soil. Here it looks like seedborn Alternaria, so your soil might be not contaminated.
I would trash all theese plants and register a complaint for the seed seller.

Again here I disagree, I do not see where you are basing this diagnosis of Alternaria, there is not a single leaf spot in these pictures?

Thanks for the responses! I didn't start them indoors, I kept them on my patio partially in the shade so the soil wouldn't dry out and have the plants die from heat from direct sunlight. I do not want to put seeds into the ground now because with these seedlings, I could get pumpkins by Christmas for pumpkin pie.

Also, can I sprinkle some granular fertilizer around the base of the plant? Will the fertilizer kill the plants at this young age?