Today was a relatively warm day. It probably got to 85 or higher here, and several of my seedlings are wilting pretty severely. I'm pretty certain that they aren' underwatered as the soil is still moist to the touch as is soil beneath the surface.

Should I be keeping them inside in a windowsill for the first year of their life?

I suggest keeping them inside a windowsill just to make sure they won't get really dry. Too much heat will greatly affect their growth.

I included a link to a really easy explanation and how to prevent it from happening again. The link is an excerpt from a seedstarting book that really helped me as a beginner figure out which seeds I wanted to start and how. I also started with a basic seedstarting kit (there are bunches out there) that gave me everything I needed--sterile soil, fertilizer, cells and cover... now I've figured out my own system but it helps to have that extra ease at the beginning... good luck!