Looks like damping off to me.
What kind of medium were they in before you replanted them? That soil looks like a lot of wood chips. Transplant can cause a lot of shock to a plant, especially such young seedlings.
you could try a small garden wire or a carefully cut and placed straw that would support the stem of the seedling
Cant see much from the pictures, but if the stem is darkening toward the bottom and growing thin... they are likely succumbing to damping off due to over watering. Not much hope in these ones pal.