Tomato help?

This year will mark our first year to attempt any kind of gardening. My husband and I have been married for 10 years, and we've lived in apartments or condos for about 8.5 of those years. So, we are very excited.

We planted tomato, pepper, and cucumber seeds in late March and they've been in our large kitchen window since then. They seem to have germinated right on schedule (our seeds came from here, for those of you who are wondering), but now some of our tomato seedlings are wilting a little. Overwatering is the only thing I can think of that might be the culprit, but I have no experience.

Here are some pictures of what's been going on:

One or two of them have some splotchy discoloration on the leaves, like this:

What do you think? Input would be very greatly appreciated by these beginning gardeners!

Edited to add: This seems to be only happening to the original seed leaves, at least so far.

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By the way, thanks for your kind words about Fiona's baptism! For those of you who were wondering, the gown was neither handmade nor a family heirloom, as much as I wish it were. It was purchased new for Elisabeth (when she was baptized seven years ago) at a little boutique-y shop. I did like that both of my daughters were able to wear the same gown. So maybe it's on its way to becoming a family heirloom!