Hello there,

There can be quite a few things wrong, ranging from soil and water PH level to poor seed quality, but I will tell you what I think is the most likely problem: Not enough sun when they were first emerging.

This is a common problem, which I myself have done all too often in the past. I still have a handful of seedlings that are about the size of yours which germinated 2 years ago in winter, but since they are unique hybrids I created, I just can't bear to throw them away. Depending on the species, lack of sufficient light in the early stages of development can range from no big deal to catastrophic. I have three suggestions:

1 - Carefully transplant the seedlings into fresh new potting soil, keep in semi-shade for about a week, then move to at least full morning sun. My advice would be different if you were in a harsh sun environment, but zone 6/7, I doubt you could give them too much, unless they are particularly shade loving species. Also, at that size, you probably want to go down to a much smaller planter, and then up-pot once the plant is at least 2-3 feet.

2 - Sow new seeds. Starting over is likely to be much faster than waiting for these to recover, which may never happen at all.

3 - Do both! (IMHO, the best option)

Also, the species of seed makes quite a bit of difference as to how to grown them. Do you know what they are?

Best of luck,
Eric