Hi Larry, a few things, how old are the seedlings,(when did you plant them)
do you still have the clear plastic lid on or over the trays/pots,or no lid on,
is the air vent open or closed, is the propagator in sunlight, or just on a table in a room,
have you pricked them out, have they a fungal problem (look for a brownring around the stem-and a white fungus) caused by to much water,
can you please give us more info
thanks
windy ;)