Looks like too much water to me. I have a rule of thumb when I grow seedlings in Winter. I don't baby them and I water them good once a week. Mine are on a south window sill and get a lot of bright light, but not direct sunlight. I use sheer curtains to prevent the sunlight coming through the window from scorching them. It can get quite warm on that window sill, so I do check for dryness. Root rot/Damping off is always a problem with seedlings.
