bigdog

Seed-starting mix is well-draining, but it also holds lots of water. Young plants need a coarser mix, something with a good amount of perlite or coarse sand in it. It wouldn't be that much of an issue if they were in a warm greenhouse or outside in warm temperatures. The combination of room temperature, indoor lighting or no direct light, and a moist medium could be doing them in. The damage you are describing sounds like the leaves are being exposed to a draft though, maybe from a vent or fan. Sort of like a wind-burn. Find a different spot for them where they will be warmer and get lots of light, and no air blowing directly on them. Good luck with them!